I said, 'I don't know exactly what happened, but let's see if I could put together an alternative story based on what I do know. Since I know that during this time period a white person and a black person could not be legally married, I know Brigham Young wasn't talking about sexual relations between two legally married people. That means fornication. To me, it seems that President Kimball's statement is very similar to what Brigham Young is reported to have said. The only difference is that Brigham Young apparently made the comments about particular divisions of the society.
Prophets normally speak on issues in which the people are having difficulty.
I find that, generally speaking, that society was very protective of the virtue of white women. If a white woman was raped, her family often killed the attacker and faced no punishment. While technically it was illegal to kill a rapist, no court would convict a white man who defended the honor of his wife, daughter, sister, or mother. In fact this attitude had prevailed in the United States until only recently. In my own non-LDS family, I had an uncle who was discovered with another woman by her husband.