Frankly, this is the first sign I've seen that Mitt Romney believes in anything but Mitt Romney.
I can definitely feel where he's coming from on the subject, too. Evangelical Christian churches have been known to burn copies of the Book of Mormon, and not just in "the old days."
I was raised Pentecostal, but in the mid-1980s I converted and was baptized into the Church of Jesus Christ of Latter-Day Saints (no, I am not still a Mormon). Not long after, I attended a "revival" at my old church. The subject was the evils of rock-n-roll, but the visiting evangelist ran an anti-Mormon ministry as well.
When someone told him that there was a Mormon in attendance, he sought me out and gave me a copy of The God Makers, a book purporting to expose the evils of Mormonism. In the spirit of reciprocity, I gave him a copy of The Book of Mormon. I was later told it ended up in the bonfire (fueled mostly by rock albums brought in by congregation members) that ended the "revival."
It didn't really bother me, but it bothered some other local LDS members a lot, even after they got it through their heads that I hadn't given it to the guy with the intention of seeing it burned, or to mark my own apostasy from the One True Faith.
The reason it bothered them so much isn't that hard to figure out.
In the mid-to-late 19th century, Mormons were regularly persecuted and driven out of numerous places where they attempted to settle (yes, I know there's more than one side to that story, but let's look at it through Mormon eyes here).
Out of New York to Kirtland, Ohio.
Out of Kirtland to the Independence, Missouri area.
Out of Missouri (with government bounties on every Mormon head!) to Nauvoo, Illinois, where the founder ("prophet, seer and revelator") of the church, Joseph Smith, was lynched by a mob.
Then west under Brigham Young, settling in Utah, followed by confrontations with the US government that stopped just short of all-out war and resulted in the suppression (eventually affirmed by a convenient "revelation") of a key church sacrament, "plural marriage."
Mitt Romney's great-great-grandfather, Parley Pratt, was murdered over Mormon polygamy. His great-grandparents were polygamists; his grandfather and father, though not polygamists themselves, were born in Mexico's "Mormon colonies" where plural marriage apparently openly continued for some time after it was suppressed in Utah by the US government.
Mitt Romney's diligently recorded family history (diligent recording of family history is a Mormon religious obligation) gives him plenty of good reasons to be sensitive to how crazy things can get when people start throwing religious texts on bonfires.
Good on Mitt.