But back to beastie's original question.
In this case I think its BY metonymic relation to the church as a whole. Why BY and not "old testament prophets?" Within Mormonism, Joseph Smith and BY are objects of much more devotion and veneration than any other prophets of any other times. Especially in Utah, BY looms large, and this is where most of the objections are coming from.
Plus, the whole incident is layered in and overdetermined by personal histories and family identifications as well--again within Utah.
Those are some of the reasons why the topic is still such a flashpoint. But, I admit its not all. Its not nearly enough to account for the foul recycling of smears against the families of the Fancher party. Reading through reactions to the PBS documentary, I encountered comment after comment like this: "What about the documented threats from that company to come back from California to destroy the Mormons?" Stories like that have no validity and never have. Juanita Brooks and those who have written after her make that clear, as did early work by Josiah Gibbs and others. One can even go back to the first investigations (Major Carleton's report is always interesting reading) to see how long ago such stories were dismissed.
And yet they persist.
First, literally every time I've seen this topic discussed by believers, the smears are resurrected. It doesn't matter how many times this has been debunked as retroactive accusations without any basis in reality, there will always be TBMs who still believe this trash. Pahoran, in particular, can be relied upon to resurrect this slander every time he participates on a MMM thread.
I do believe the reaction of TBMs to MMM has to do with their reverence towards BY and Joseph Smith, and with the fact that TBMs do possess the normal moral reactions of other people, and have to deliberately work to neuter those normal reactions when forced to.
That's an awkward sentence so I'm going to try to clarify with another example.
TBMs, like the vast majority of other human beings, have an instinctively negative moral reaction to the idea of a man "taking" other men's wives - whether to simply have an affair, or to induce them to leave their husband for himself. And yet apologists vigorously defend Joseph Smith' behavior on this point.
They have been forced to because the evidence is overwhelming on this point. So, because they are True Believers in the Eric Hoffer sense of the word - people whose entire identities are so bound up in their belief system that it is far too threatening to stop believing so any amount of mental gymnastics will be engaged in to enable belief to continue - they have "neutered" their normal moral reactions and constructed an apologetic defense of his behavior.
In the same way they would construct an apologetic devise to enable them to continue believing if the evidence that BY actually ORDERED MMM was just as overwhelming.
What I think this demonstrates is that the same people peddling this apologia are only convinced by it because they have to be. Otherwise, they would offer this sort of defense
before being forced to.
Each and every time the apologists have constructed defenses against the most controversial aspects of Mormon history - Joseph Smith' treasure digging, his polyandry - before the overwhelming evidence was clear, the same apologists would argue vociferously
against the possibility that the event even occurred - just like they do today with BY's involvement in MMM. Remember back in the day when a notable apologist - I believe it was Nibley - said that if real evidence came out that Joseph Smith had been convicted of money digging it would be devastating for church claims? And yet when that evidence was, indeed, discovered, apologists simply constructed mental gymnastics to justify it.
Do any of us doubt that, if the evidence that BY ordered the massacre was indisputable, that apologists would construct explanations and defenses of the action?
The fact that they are not offering these musings when the evidence is
not indisputable demonstrates that the future defenses are artificial constructs, designed not out of logic and moral reasoning, but out of necessity to salvage belief.
The fact that apologists weren't justifying Joseph Smith' polyandry and money digging before the evidence was clear and it was only a possibility demonstrates the same fact to me - that these defenses are not based out of logic and moral reasoning (which the apologists possessed and were using prior to the overwhelming evidence) - but simply out of necessity to salvage belief.