I don’t think just by watching Steven Universe or collecting some Warhammer little figures makes you one or another type of person. However, from my experience, the people who always harass these fans (especially those who go after the “SJW” for no reason) are usually people dedicated to watch and analyze every anime, even those that have an insane amount of repetitive lines and fanservice. You eventually get some clues of what type of person these people are. The avatar, how they comment some news based on their preferences, how they answer to other people, etc.
I don’t think every anime fan is like this, but this is something they wouldn’t like to admit. It’s pretty easy for them to get snidey to someone who didn’t find an anime enjoyable. Not to mention, whenever you are positive about something for logical reasons, they would come back to say “so if you like this, why didn’t you like this other thing you said it was trash?”.
I think this is how these people survive. Because in the anime community there’s no bad reputation regardless of their actions.
Besides, it’s so easy not to be a dick. Just don’t. Be nice to other people.