How would you describe a reactionary? What thought-processes and decisions (contrasted with Marxist thought) define one?
The clue is in the name, reactionaries arise in reaction to the progressive force of history (i.e. the class conscious proletariat) in an attempt to preserve current power structures.
I don’t necessarily think there is one “thought process” that defines a reactionary, reactionaries are different in different material conditions. In revolutionary France, a monarchist was reactionary and the bourgeois democratic forces were progressive. In the current epoch, bourgeois democratic forces are reactionary. In a future socialist society, there would be reactionary elements of a different type (vestiges of capitalism that want to return to a market economy, perhaps).
The most dangerous and fundamentalist of the reactionaries are of course the fascists, but they aren’t the only group that is reactionary in current conditions.
I suppose if I was to touch on the thought process/decision making part of your question, I would say that most reactionaries A. Have no theory of class, or an extremely crooked and non-Marxist theory of class, B. Have an idealist concept of history, C. Are usually bound by the limits of capitalist realism in their conception of the ideal society. This leads them into all sorts of incorrect analytical analyses and decisions.
My understanding was a form of political thought that exists purely in reaction to another political vision or specific progressive change. For example being anti-vaccine is a reactionary position because the only coherent part of it is a political goal that you don’t want to take the vaccine. There is no positive political vision. Communism exists in contrast to this because you begin with the goal of a classless, stateless society and then you apply materialist dialectics to the material conditions of the state you exist within to try and achieve that. This is just my understanding and I would be pleased to hear from a comrade if I’m wrong.
When I put mentos in coke there's a pretty strong reaction idk
-7DeadlyFetishes
A reactionary is often described as a conservative, someone that wants to protect some status quo or tradition against change. This is inadequate and we already have a name for that (conservatism). A reactionary goes beyond this and pushed violently against left action even if they are not trying to preserve or conserve a way of being, policy, tradition, etc. Nazis were reactionary, a response to the left that used some mores of tradition but really sought a resolution to the crises or capitalism for part of the ruling class, scapegoating and sacrificing the rest. They did not try to conserve overall, they sought a "third way" that maintained capitalism, capturing both anti-left sentiment and populist sentiment.
So, the defining aspect of reaction is that they are a response to the left, and push back on it hard, regardless of how close their own goals hew to the status quo. A reactionary might want to nuke half the planet if it means the end of communism. A reactionary justifies all violence done to socialists and joins their efforts to it, even if it's a fundamental violation big what they claim to hold dear (e.g. rule of law). A reactionary is the vicious chud who misogynistically attacks AOC because she is perceived as a left icon and the best he can do is chuckle at "AOC is stupid" memes.
A short and sloppy answer... When somebody's political belief is only to "make them cry", I tend to view that as reactionary. Their only criteria for "winning" is only to hurt somebody else.
A reactionary wants to preserve the current world order, regress to an earlier one, or somehow combine the two. They react to changes which would harm this world, but never advance any changes.
Someone who resists progressive ideas in an immediate and reflexive way. Where its clear they are being guided by fearful instincts and have resisted the idea of thinking about an idea further. When questioned, they become even more adamant and refuse further critical discussion or thought.
I like the term because it makes me think of conservatives chimping out like animals over new ideas.