Everyone's a constitutional lawyer on FR.
As far as I know, there is no case law at all on this matter. But, for example, Michael Levin at City College of New York has written books about the genetic inferiority of blacks. No doubt his status as a professor gives those books legitimacy. CCNY tried to prevent Levin from teaching required courses; Levin took them to court, won, and got costs.
One lower court ruling under a bit different circumstances. There was no individual claiming they were damaged by his discrimination, which might have changed the outcome of that case. Interesting that he won though. Letters of recomendations have been the grounds for many lawsuits in employment circumstances. I don't think anyone is dumb enough to try it in todays environment.
Levin can write all the books he wants he just can't post on his state paid for website that he will discrimiante against blacks. If he does that he will lose in court.