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. He's a reactionary but he diagnoses some of the problems of modernity correctly. He articulates the appeal of the heroic or mythic and the dearth of that in bourgeois society. The Ubermensch (not necessarily the Nazi ideal) is a reactionary response to the crisis of the death of God that needs to be overcome (ironically, I can't think of a better term off the top of my head than 'overcome', so even in my critique I'm still operating within Nietzschean terms).