The difference is that when all the communists aggressively like each others' posts, they don't sort themselves to the top, and when I make a comment it isn't hidden from view until it gets removed by the moderators. Reddit filters the angriest and most hateful subset of any big enough subreddit to the top by algorithm, and then moderation is as often an exacerbating factor as it is a correcting one. It doesn't even have to be political: top comment of r/relationships is almost always the person most heartlessly dismissing everyone the OP loves. "Anger is the devil's cocaine", and you can find more of it there to drink up with every single click.