CalBuzz, one of my favorite political sites, has an interesting essay on what the anti-Mormon sentiment in America means for Mitt Romney.  Among the central points:
Gallup found that Democrats (27%) were more unlikely to support a Mormon than were Republicans (18%) – suggesting that in a general election, a Mormon’s hard-right views on gays, marriage, abortion and women’s rights might have more to do with resistance to an LDS candidate than religion itself.
Actually, not all politically active Mormons share that "hard right" approach -- Stew Udall, t he Arizona environmentalist, Congressmember and interior secretary under Kennedy and Johnson was a Mormon. So was his brother Mo, a liberal member of Congress who ran for president in 1976 as a left alternative to Jimmy Carter. But like evangelical Christians, Mormons in general tend to be conservative, especially on social issues.
The CalBuzzers are puzzled by the distrust of this particular religion:
It’s hard to determine what, exactly, drives anti-Mormon sentiments – whether it’s what people know, what they don’t know or what they think they know.
Are they familiar with Joseph Smith, Jr., the treasure digger from Palmyra, New York, who said he was visited by the angel Moroni in 1827 and guided to a box of golden plates which he said contained what is now known as the Book of Mormon, after he transcribed them from “reformed Egyptian”?
Are they thinking about the breakaway Mormons in HBO’s late great "Big Love"  with Bill Paxton, Jeanne Tripplethorn, Chloe Sevigny, Ginnifer Goodwin, Bruce Dern, Mary Kay Place and Amanda Seyfried? Maybe they think Mormons are all like Roman Grant, the evil self-proclaimed prophet and leader of the Juniper Creek Compound played by Harry Dean Stanton.
Or are they like one wag we know who argues that the only difference between Mormonism and Scientology is the choir?
If you want to pounce on logical improbabilities in religions, you’ve got your parting of the Red Sea and the burning bush, the immaculate conception and the resurrection and that passel of virgins waiting for you in Heaven. Pick your myth.
The point, of course, is that the stuff Mormons believe is no odder than the teachings of most major religions. But there's a big difference, and I find it fascinating.
The thing is, if you believe in Jesus or Abraham or Mohammed, you're talking about people who lived a really long time ago, before there were accurate written records. Despite former Guardian writer Burton Wolfe's best efforts , you can't really prove that Jesus lived or didn't live, or did or didn't turn water into wine or cure lepers. The Bible has been translated so many times (and by many accounts, rewritten so many times) that it's hard to know exactly what the original stories even were.
On the other hand, there are people alive today whose grandparents might have known Joseph Smith. Mormonism came to life in a time of newspapers and nearly-modern record keeping. Upstate New York in 1827 wasn't exactly Manhattan today, but it wasn't the Middle East in 44 B.C. either. There are still accounts of newspapers of the day denouncing Smith as a charlatan and fraud. Nobody can argue about whether he was into polygamy or not.
In the context of the 1800s, although there was plenty of strange religious stuff going on, the notion of a failed treasure hunter finding golden plates left by an angel (who then took the plates back after Smith made the one and only translation) seems pretty bizarre. That's in part because the traditional religions all teach that the weird shit took place a really long time ago, which somehow makes it easier to justify.
If the son of a carpenter announced in 1827 that he was really the son of God, and that his mother was a virgin who had been impregnated by something called the Holy Spirit, who was also sorta, kinda part of God, isn't it likely he might be called a nutjob? Ya think?
And the way the Mormon Church operates, with all of its official secrecy, just encourages people to think of it as a cult. But you ever tried really looking into the Vatican?
My point is that poor Mitt is going to face an uphill battle over his religion largely because the stuff that's really, really hard to believe supposedly happened a couple millenia after stuff that's really, really hard to believe was supposed to happen.
Not defending the Mormons here. (Although, if you stipulate that women have equal opportunity and gay people can get married, too, what IS wrong with polygamy? )