First, let me say I've known a lot of Mormons.  Most were decent people.  Some have been or are good friends.  Most of them have very little idea about the details of the Mormon history or teachings.  Basically, they are like the sheep of nearly every major religion... they believe what they are taught, some of it they remember.  The Mormon church has made great efforts to conform to beliefs of the United States, so that they they are less objectionable to the general public. In a way, the Mormon church has become institutionalized, like most other Western religions.  And, like most older Western religions, they hope some of their past doesn't come back to haunt them.  I think. Lack of discussion and defense on their part is what makes me believe this to be true.

But I also understand how true believers of any religion function.  They study the teachings themselves, often not relying on other believers for guidance.  Do they disregard some passages of text from their founders? Not likely. Do some religions have passages from their venerated texts that are not compatible with the US version of a free and tolerant society? Yes, many.  Maybe all. Does the Mormon religion have some teachings that would shock the public? Yes. Do very many people know? No. Does the Mormon church defend or denounce these teachings? Not that I've found so far. Even non-Mormons don't want these issues surfaced.  It is fodder for trouble.  There is no happy solution other than to let the sleeping dogs alone on both sides of the fence. Most Mormons won't change.  Some may decide they don't believe anymore.  Some will stubbornly believe. Most will forget about it. The trademark of every religion.
Yes, I didn't mention what could be so awful.  I'm not trying to start that fight. If you are interested, you can find some things for yourself.  Try searching for "blood atonement" in the Journal of Discourses on the LDS website. I'm not God's confidant, so I can only judge the compatibility of codified religious intolerance.  It kind of boils down to a question of what do the "true believers" think.

Is Romney a true believer, or a conventional or typical believer? Remember that "true believers" are usually hard to find in any religion.  Most are just followers. If he is a true believer, what does that mean, and what are the implications of him being a President?
Romney may possibly be the most solid conservative political candidate.  Yet what is his ultimate allegiance? Could a higher allegiance ever adversely impact his decisions as a President?
I hear people comparing worrying about a Mormon to worrying about Protestants and Catholics distrusting each other. The Protestants and Catholics have their problems, but their problems aren't usually about mysterious physically dangerous teachings. 
The Mormon religion is vastly different than Protestants and Catholics. The Mormon church has cozied up with a largely Protestant United States. I think they did it because they saw the need, not because they "saw the light".  If the Mormon church is truely institutionalized as a religion compliant with the generally accepted moral and ethical codes of the United States, we should have nothing to worry about.  Should.

As an observer on this planet, I see a lot of effort by people that are not Mormon to try to convince the public that being Mormon is the same as most of the rest of the population.  As usual with most religions, the typical followers of many religions are similar to each other in a given culture.
Should some issue ever come up that requires a choice between some unknown and unfamiliar Mormon precept or a typical "American" response, will Romney respond as a typical American, or does he have a higher allegiance, and could there be a conflict of interest? Should anyone ask him, or are we too desperate to convince ourselves of his "sameness"?
We also, as a collective society, desperately want religions to be the same.  They are not.  They may behave similarly in their typical daily activities.  Their typical followers may be nearly indistinguishable from the typical followers of other religions. But the deeply embedded "lifeforce" of many religions are vastly different.  Only the "true believers" understand those differences. And only the "true believers", and some under their influence, act on those differences.

Good luck, people of planet earth. Don't wake up the dogs.