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
And the Paul Schrader movie about his life is my favourite film. Beautifully shot dissection of the pathologies that made him a fascist.