These are more or less controversial, but range from not outside the Overton window at all (saying that factory farming is immoral) to being a little outside. But they are by no means “taboo” in the sense that you would face serious social cost for expressing them. Saying “there are heritable statistical group differences in mean IQ” is on a completely different level. People had their careers ended and reputation ruined because of this. In comparison, saying that golf courses should be replaced with apartments carries almost zero personal risk.
My issue is with the specific takes Cremieux has and ways he acts, which are racist, and harmful, and bad.
I think it is defamatory, bad and counter to the spirit of rationalist discourse to accuse someone of racism when they have put forward an empirical hypothesis including evidence to back it up. The term “racist” has an implication of being merely based on an irrational prejudice, which is clearly not the case for Cremieux.
I’m saying that it is a serious accusation, whose consequences are far more impactful (e.g. possible career end) than ones feelings being hurt. So one should be extra careful before making the accusation. In case of Cremieux we know that he is in fact defending an empirical hypothesis, and he has provided an extensive amount of evidence and arguments in its favor (e.g. on his blog). This provides strong reason to think that the accusation of racism is not justified.