I'm not sure that knee-jerkingly smearing him (by association) as a racist eugenicist quite disproves the point that tenure is not protection from misguided attacks.
Shockingly, very few things protect you from people saying bad things about you on the Internet.
No need to turn to his associations for evidence, you're free to read his work and judge for yourself.
The whole point of character assassination is to make people less likely to actually read it.