Today I stumbled across a book called A World Without Jews, by Karl Marx. It's pretty horrible stuff. It occurs to me that I can't think of really horrible stuff written by any of the thinkers I greatly respect. Of course Schopenhauer's stuff on women is terrible, but I don't have that much respect for Schopenhauer. Heidegger was a Nazi, but I also think he was a terrible philosopher.
On the other hand, I have heard that, for example, Frege had some pretty disturbing views. I don't know if he published any of them. I can't think of anything published by the thinkers I love which is comparably disturbing. But my memory is probably being selective; I would prefer not to remember such things. I wonder what I'm forgetting.