Here's more context for Coe's remarks:
Well, in fact I'm a totally irreligious person, even though I was born and raised a perfectly good Episcopalian Christian. Yet figures like Joseph Smith fascinate me as an anthropologist, and I suppose as an American, too. When I read Fawn Brodie's wonderful book, No Man Knows My History, I couldn't put it down. I mean, it's the most exciting biography I've ever read.
When I did read it for the first time, I realized what kind of a person this Joseph Smith was. In my opinion, he was not just a great religious leader; he was a really great American, and I think he was one of the greatest people who ever lived. This extraordinary man, who put together a religion -- probably with many falsities in it, falsehoods, so forth, to begin with -- eventually came to believe in it so much that he really bought his own story and made it believable to other people. In this respect, he's a lot like a shaman in anthropology: these extraordinary religious practitioners in places like Siberia, North America among the Eskimo, the Inuit, who start out probably in their profession as almost like magicians doing magic. ...
I really think that Joseph Smith, like shamans everywhere, started out faking it. I have to believe this -- that he didn't believe this at all, that he was out to impress, but he got caught up in the mythology that he created. This is what happens to shamans: They begin to believe they can do these things. It becomes a revelation: They're speaking to God. And I don't think they start out that way; I really do not. ...
It's as though P.T. Barnum had started to believe his own fakeries. In many respects he was a great man, [and] he could have done something of the same thing, but he didn't. He didn't have this kind of inner spirit and this sense of destiny that Joseph Smith had. Joseph Smith had a sense of destiny -- and most fakers don't have this -- and this is how he transformed something that, I think, was clearly made up into something that was absolutely convincing, convincing to him and to a lot of people, and he never could have convinced a lot of people if he hadn't been convinced himself.
http://www.pbs.org/Mormons/interviews/coe.html
Now I'm not sure how Coe goes to "one of the greatest people who ever lived", but Joseph Smith was definitely a religious genius, and the religion he created has had an impact on the history of the US at the very least. If the LDS church continues to grow and continue to amass great wealth, and exercise its influence in the political arena of not just the US but other countries, it could conceivably even extend its influence.
Normally when believers refer to the great things Joseph Smith has done, they are talking in terms of religious claims - the restoration of the only true priesthood authority of JC to perform saving ordinances.