I suspect you are describing a real phenomenon. There is a reason that racial preferences for blacks don't usually attract much in the way of strongly argued conservative opposition. We oppose racial preferences, but are relieved when the subject is changed. Pressing the RACISM button doesn't make conservatives jump like it used to, but it still makes some of us uncomfortable.
One thing I like about your theory is that it leaves us some hope that this is still basically a center-right country. So does my preferred theory of the reason for the disaster, though mine is much less original:
June 2012 Gallup Poll: Bias Against a Mormon Presidential Candidate Same as in 1967
10% of Republicans, 18% of Independents, and 24% or Democrats said they would not vote for a well-qualified Mormon candidate for president.
One thing stood out in that link. Of those who didn’t know Romney’s religious faith in June, 29% said they wouldn’t vote for a Mormon.
Has this poll been taken with regards to Buddhists, Hindus and Mohammedans. Of course they’ve voted one of the latter ones into office not knowing he is a Muslim, and I suspect would have, had they known, only because he is a saintly ‘African-American’.
I'll guess they didn't, because the no-vote numbers would have been much lower for Blacks.