They can always say that Brother Brigham was speaking as a man, and not as a prophet, when he forbade mixing of the races. They can say that his discourse was never published in the D&C. They can say that President Young never actually executed any LDS white man for having intercourse with a black woman.
So -- if we could sent Elder Romney and Apostle Holland back in time, in our wayback machine -- would they have the guts to stand up to Brigham Young and denounce him and his racist teachings?
"Thus sayest the Spirit, unto my former servant Brigham: Thou hast pronounced false doctrines and thy words are of Satan that old Deceiver. No man shall be put to death in the Camp of Israel, merely for mixing his seed with a woman of a different color -- no more than Moses was admonished for taking to wife an Ethiopian woman. Henceforth and forever, amen and amen."
Yep, they can say that. The beautiful thing is, in the court of public opinion, non-Mormons don't split hairs. He said it, and Romney's troubles have really just begun, now that he is wrapping up the nomination. This circus is going to make Jeremiah Wright look like a choir boy.