Here's a collection of official teachings from the LDS Church from now and during the last thirty years. They include teachings from all parts of the church - general conference, current lesson manuals, church magazines, official pamphlets, popular books and even Family Home Evening guides.
Read for yourself.
Notice how often they refer to Alma 39:5 and re-testify that sexual "impurity" is next to murder.
"Why is this matter of sexual relationships so severe that fire is almost always the metaphor, with passion pictured vividly in flames? What is there in all of this that prompts Alma to warn his son Corianton that sexual transgression is 'an abomination in the sight of the Lord; yea, most abominable above all sins save it be the shedding of innocent blood or denying the Holy Ghost'? (Alma 39:5)."
-Apostle Jeffrey R. Holland, "Personal Purity," New Era, Feb. 2000, page 4
“Touch Not Their Unclean Things. Too many Latter-day Saints today somehow believe they can stand with one hand touching the walls of the temple while the other hand fondles the unclean things of the world. We can’t do that. As Alma said, “Touch not their unclean things” (Alma 5:57). I plead with you, put both hands on the temple. Put your arms around the temple, and hang on for dear life to your family dream. If you don’t, the tigers will come at night and tear your dreams apart."
"....show your profound respect for that love—and for the doctrines about eternal love and family life—by bridling your passions. Don’t be deceived by the false idea that anything short of the sex act itself is okay. That is a lie, not only because one step overpoweringly leads to another, but because even touching another person’s body with sexual intent is part of the intimacy that is kept holy by the sanctuary of chastity. Please also beware of unnatural sexual acts that are just as immoral, if not worse, than traditional fornication or adultery."
- Elder Bruce C. Hafen, “Your Longing for Family Joy,” Ensign, Oct. 2003, page 28
"We desire with holy zeal to emphasize the enormity of sexual sins. We hold that sexual sin is second only to the shedding of innocent blood in the category of personal crimes. Though often regarded as insignificant by those not knowing the will of God, they are, in his eyes an abomination, and if we are to remain his favored people they must be shunned as the gates of hell. The evil results of these sins are so patent in vice, crime, misery and disease that it would appear that all, young and old, must perceive and sense them. They are destroying the world. If we are to be preserved we must abhor them, shun them, not practice the least of them, for they weaken and enervate, they kill man spiritually, they make him unfit for the company of the righteous and the presence of God.
- Prophet Joseph F. Smith, Teachings of Presidents of the Church: Joseph F. Smith, 18: Chastity and Purity, From the Life of Joseph F. Smith Lesson Manual, page 155, Published and taught during 2000-2001 Church-wide Priesthood and Relief Society classes
"If we pollute our fountains of life, there will be penalties 'exquisite' and 'hard to bear' (see D&C 19:15), more than all of the physical pleasure ever could be worth. Alma told his son Corianton, 'Know ye not, my son, that these things are an abomination in the sight of the Lord; yea, most abominable above all sins save it be the shedding of innocent blood or denying the Holy Ghost?' (Alma 39:5.) The code for moral law is found in the scriptures, stated as simply as, 'Wickedness never was happiness.' (Alma 41:10.) The scriptures speak in general terms, leaving us free to apply the principles of the gospel to meet the infinite variety of life. But when they say 'thou shalt not,' we had better pay attention.
-Boyd K. Packer, "Our Moral Environment," Ensign, May 1992, page 66
"God has placed foremost in the category of serious crimes against which we are warned... first, murder, and second only to that, sexual impurity. The Church counsels you to be modest in your dress and manner and to forbid the evil thoughts that would prompt your lips to obscenity and your conduct to be base and unseemly. One day [we] will have to meet our Maker and as Moroni put it - and this is pretty strong language - he said, 'Do you think that you could be happy in the presence of the Holy One of Israel with a sense of guilt of your own uncleanness?' He said, 'You would be happier to live with the damned souls in hell than in the presence of the Holy One of Israel with your uncleanness and your filthiness still upon you.'"
-Prophet Harold B. Lee, The Teachings of Harold B. Lee, p. 213-14, 2002-2003 lesson manual for all Church-wide Priesthood and Relief Society classes
"In the Book of Mormon, the prophet Jacob tells us that the Lord delights in the chastity of His children (see Jacob 2:28). Do you know that, my brothers and sisters? The Lord is not just pleased when we are chaste; He delights in chastity. Mormon taught the same thing to his son Moroni when he wrote that chastity and virtue are 'most dear and precious above ALL things' (Moro. 9:9). You may discover to your horror that what you should have saved you have spent, and that only God’s grace (the Church) can recover the virtue you so casually gave away. On your wedding day the very best gift you can give your eternal companion is your very best self - clean and pure and worthy of such purity in return."
-Apostle Jeffrey R. Holland, "Personal Purity," New Era, Feb. 2000, page 4
"You will recall Alma’s teaching his son Corianton that unchastity is the most serious offense there is in the sight of God, except for murder or denying the Holy Ghost. (See Alma 39:5.) President Clark, in a conference address in October 1938, said: 'Chastity is fundamental to our life and to our civilization. If the race becomes unchaste, it will perish. Immorality has been basic to the destruction of mighty nations of the past; it will bring to dust the mighty nations of the present. You young people, may I directly entreat you to be chaste. Please believe me when I say that chastity is worth more than life itself. This is the doctrine my parents taught me; it is truth. It is better to die chaste than to live unchaste. The salvation of your very souls is concerned in this.' (In Conference Report, Oct. 1938, pp. 137-38). Now, my dear friends, we know there is nothing new in what we have said. These things are time-tested; they are true. To this we testify"
-First Presidency Message "We Believe in Being Chaste," Ensign, Sept. 1981, page 3
"One of the most solemn statements about being chaste is that of Alma to his son Corianton: 'Know ye not, my son,' he said, 'that these things are an abomination in the sight of the Lord; yea, most abominable above all the sins save it be the shedding of innocent blood or denying the Holy Ghost?' (Alma 39:5). Very few of us will ever be guilty of murder or of the sin against the Holy Ghost. But the law of chastity is frequently broken and yet it stands next to these other sins in seriousness in the eyes of the Lord.
-Prophet Ezra Taft Benson, "The Law of Chastity," Ensign, Oct. 1988, page 36
"Among the most common sexual sins our young people commit are necking and petting. Not only do these improper relations often lead to fornication, [unwed] pregnancy, and abortions - all ugly sins - but in and of themselves they are pernicious evils, and it is often difficult for youth to distinguish where one ends and another begins. They awaken lust and stir evil thoughts and sex desires. They are but parts of the whole family of related sins and indiscretions. Almost like twins, 'petting' and fornication are alike."
-Prophet Spencer W. Kimball, The Miracle of Forgiveness, page 65 - popular book for Bishops to use when counseling members
"On the very brink of sorrow and disgrace are they who are guilty of immodesty, necking, petting, or other secret and unwholesome practices. Neither person is at his best when he is petting. Each discovers in the other and reveals in himself traits of which he should be ashamed. He is voluntarily permitting himself to be led down the path of misery and shame. Some pride themselves on never going further than petting. They do not realize how disastrously far they have already gone."
-Apostle Hugh B. Brown, The Abundant Life, page 64
"Petting is indecent and sinful, and the person who attempts to pet with you is himself both indecent and sinful and is likewise lustful... Is that what you want? Will you not remember that in the category of crime, God says sex sin is next to murder?"
-Apostle Mark E. Petersen, General Conference, 3 October 1956
Alma told his wayward son Corianton, who had gone after the Lamanite harlot Isabel: 'Know ye not, my son, that these things are an abomination in the sight of the Lord; yea, most abominable above all sins save it be the shedding of innocent blood or denying the Holy Ghost?' (Alma 39:5.) Sometimes we give as reasons for the law of chastity the risk of pregnancy or abortion, the possibility of an unwanted or embarrassing marriage, or the chance of a terrible venereal disease. As serious as these things are, I’m not sure they are the fundamental reason for the Lord’s having placed this commandment ahead of armed robbery, fraud, and kidnapping in the seriousness of sins. Think of it - unchastity is second only to murder. Perhaps there is a common element in those two things - chastity and murder.
-Elder Bruce C. Hafen, 'The Gospel and Romantic Love,' Tambuli, June 1983, page 23
"The prophet Alma grieved because one of his sons had broken the law of chastity. Alma said to his son Corianton, 'Know ye not, my son, that these things are an abomination in the sight of the Lord; yea, most abominable above all sins save it be the shedding of innocent blood or denying the Holy Ghost?' (Alma 39:5). Unchastity is next to murder in seriousness."
- Gospel Principles Manual, Unit Eight: FAMILY SALVATION, 39: THE LAW OF CHASTITY, page 247, Manual used today in church-wide Gospel Doctrine classes
"Relate the story of Corianton, one of Alma’s sons, in Alma 39:3-4. Discuss how he sinned by forsaking his ministry and going after Isabel. Point out that he broke God’s law of chastity. Read together what Alma said to Corianton in Alma 39:5. Discuss why sexual transgression is such a serious sin."
-Current Family Home Evening Resource Book, LESSON IDEAS, CHASTITY, page 177
"Why can’t someone go into a missionary training center or into the mission field, repent of sins, and fix the problems there? Perhaps the best answer to that question is 'Because the Lord says you can’t.' The First Presidency has given clear direction that this will not be the case. What does it mean to be totally clean? It means that you would never be involved in the serious transgression... or any other sexual activities, or even transgressions of perhaps a lesser degree, but still of great seriousness, such as petting, (masturbation) or pornography of any kind. It means we must shun immodesty, flee from bad thoughts, and avoid even the appearance of sin."
"Several weeks into his mission, in total agony for his sins, (a missionary) confessed them to his mission president. What a sad experience! He felt greatly relieved that he’d finally confessed, but with all his heart wished he had done so earlier. With great sadness for all, the young man was sent home. One can only imagine the pain, humiliation, and regret. How his parents and family wept! How the heavens must have wept!"
-Elder Gene R. Cook, "Worthy to Serve," New Era, May 1994, page 4, widely distributed to new missionaries entering the mission field
"And Cain said unto the Lord, My punishment is greater than I can bear. Behold, thou hast driven me out this day from the face of the earth." (Genesis 4:9-14.) That was true of murder. It is also true of illicit sex, which, of course, includes all petting, fornication, adultery, homosexual acts, and all other perversions. The Lord may say to offenders, as He did to Cain, "What hast thou done?" The children thus conceived make damning charges against you; the companions who have been frustrated and violated condemn you; the body that has been defiled cries out against you; the spirit which has been dwarfed convicts you. You will have difficulty throughout the ages in totally forgiving yourself."
-Prophet Spencer W. Kimball, "Love Versus Lust", BYU Speech January 5, 1965. Often-used quote still used today in LDS seminary classes.
"I do not find in the Bible the modern terms "petting" nor "homosexuality," yet I found numerous scriptures which forbade such acts under by whatever names they might be called. I could not find the term "homosexuality," but I did find numerous places where the Lord condemned such a practice with such vigor that even the death penalty was assessed."
-Prophet Spencer W. Kimball, "Love Versus Lust", BYU Speech January 5, 1965.
"The early apostles and prophets mention sins which seemed completely reprehensible to them. Some of them were adultery, being without natural affection, lustfulness, infidelity, incontinence, filthy communications, impurity, inordinate affection, inventors of evil things. Today we call them necking, petting, fornication, sex perversion and masturbation. Included are every hidden and secret sin, and all unholy and impure thoughts and practices. Next to the unpardonable sin (of murder) come the diabolical crimes of sexual impurity which raise their ugly heads in many different forms, including aberrations of self-pollution (masturbation) and the abhorrent and unnatural practices involving other people (petting, fornication, homosexuality)."
- First Presidency Pamphlet, "To The Returning Missionary", Page 11, still distributed today to most Returned-Missionaries.
"A boy whom the apostle (Spencer W. Kimball) a week back had turned down for a missionary recommend, wrote that he had resisted petting with his girl, and was determined to justify the apostle's confidence in him. And a young girl wrote him thanks for his counsel the week before, continuing: "I know with your (Spencer W. Kimball) blessing and your prayers I will overcome my weaknesses. Pray for me, please. It seems easier to have some help. I hope there are few in this world like me. I often wondered why the Lord didn't destroy me for all the things I've done."- Biography of Spencer W. Kimball, Chapter 15.
"To keep the Children of Israel from committing these sins, the Lord proceeds to name them and to prescribe penalties for their commission. I am going to name a few of them. First is incest. I am not enlarging on it. In the law incest included more than we now ascribe to it. It included marriage between people within prohibited relationships. The penalty for incest was death to both parties. Fornication-sometimes adultery and fornication are used interchangeably. But for most kinds of fornication, the penalty was death. For adultery, it was death for both parties. For homosexuality, it was death to the male and the prescription or penalty for the female I do not know."
- Apostle J. Reuben Clark, Jr., Conference Address, April 8, 1957.
"Prophets anciently and today condemn masturbation. It induces feelings of guilt and shame. It is detrimental to spirituality. It indicates slavery to the flesh, not that mastery of it and the growth toward godhood which is the object of our mortal life. Our modern prophet has indicated that no young man should be called on a mission who is not free from this practice. What is more, it too often leads to grievous sin, even to that sin against nature, homosexuality. For, done in private, it evolves often into mutual masturbation-practiced with another person of the same sex and thence into total homosexuality...."
- Prophet Spencer W. Kimball, "The Miracle of Forgiveness, Pages 77-79, 81-82.
"If adultery or fornication justified the death penalty in the old days, and still in Christ's day, is the sin any less today because the laws of the land do not assess the death penalty for it? Is the act less grievous? There must be a washing, a purging, a changing of attitudes, a correcting of appraisals, a strengthening toward self-mastery. There must be many prayers, and volumes of tears. There must be an inner conviction giving to the sin its full diabolical weight. There must be increased devotion and much thought and study. And this takes energy and time and often is accompanied with sore embarrassment, heavy deprivations and deep trials, even if indeed one is not excommunicated from the Church, losing all spiritual blessings."
- Prophet Spencer W. Kimball, "The Miracle of Forgiveness, Page 155
"How like the mistletoe is immorality. The killer plant starts with a sticky sweet berry. Little indiscretions are the berries -- indiscretions like sex thoughts sex discussions, passionate kissing, pornography. The leaves and little twigs are masturbation and necking and such, growing with every exercise. The full-grown plant is petting and sex looseness. It confounds, frustrates, and destroys like the parasite if it is not cut out and destroyed, for, in time it robs the tree, bleeds its life, and leaves it barren and dry; and, strangely enough, the parasite dies with its host."
- Prophet Spencer W. Kimball, General Conference Address, April 1, 1967.