Also, I don't just mean they are reactionary in certain area or in their personal life (Like Aristotle was important for biology despite being an apologies for slavery)?
I mean worth looking into their thinking precisely in areas where they're reactionary.
Possible suggestions (not saying they're justified) that I expect people would put forward include:
- Carl Scmitt
- Heidegger
Nietzsche is legitimately probably my favorite prose writer, and Genealogy of Morals is great and useful, philosophically. But yeah it's like every other line is something insightful and interesting, but the next line is usually disgusting. I like to read him and pretend that he is being sarcastic, like making fun of his readers who buy into his fawning over greatness and believe that these lines are meant for them. But I'm pretty sure they're not.
A decent familiarity with Nietzsche is useful since he was so influential, and on the left writers like Foucault that were largely inspired by Nietzsche and his WtP theory, get passed around and discussed a lot. So its useful to understand critiques of Nietzsche which translate to critiques of later writers. Nietzsche is also really good at turning a point around to make it seem ridiculous, the legacy of which is found in a lot of reactionary skepticism and gish-galloping, even though most reactionaries claim to hate him ("God is not dead :frothingfash: .")