I had something similar happen to me in r/republican. Pre-Trump, it actually wasn't a bad subreddit. You could have relatively civil discussions in there. I often used it to see and ask how Republicans/Conservatives thought about various things. I always tried to be respectful, understanding that that the wasn't "my sub." I flaired myself with a 'D' or something so it'd be obvious that I wasn't hiding and trolling. Had some OK discussions in there the few times I'd dare to chime in.

But it changed once Trump started running. I once was having a civil discussion with a user, trying to understand their take, and ended up linking to an article from a large, mainstream publication, to show what I was talking about.

I was banned with no comment. When I politely asked mods what I did wrong and if I could be unbanned if I promised to not do whatever I did again, I got the message: "Don't link liberal sources." And it wasn't a liberal source! Just something not from Fox or wherever. From then on, I could lurk, but I could never comment.

And the mods got crazier. I'd see that they'd remove comments and ban anyone, even Republicans, who spoke out against Trump. At that point, there was no reason to go there anymore.