"I would tell him he has a great shot, as he would then gain a great deal of attention if he actually had credible evidence and countered the previous evidence convincingly." Yes, just like Larry Summers received when he suggested that genetics MIGHT play a role in why so few women are in sciences

The key weasel phrase is "credible evidence." And yeah, it would be tantamount to career suicide for any humanities PhD student to argue in his dissertation that the internment of Japanese Americans was a good idea. (Maybe he could get away with it if he were Japanese.)

Many, perhaps most cultures and subcultures have taboos. In Thailand, you don't insult the King. In Saudi Arabia, you don't insult Islam. And in the American Academy, you don't say anything which might be construed as racist.