The hivemind kills me. Especially in subs like /r/politics, where people will take your head off if you aren't a big government, Obama loving liberal - and there is nothing wrong with being a big government, Obama loving liberal, and I love to debate with those people. Not so much when they scream at me for my political alignment.
Last time it happened to me was when I was using RES to tag people based on their self-proclaimed professions. Whenever I found someone I'd tagged profoundly in the negative in a conversation, I'd make a concerted effort to keep the conversation going by appealing to their career and approaching the conversation with an implicit understanding of where they're coming from. When everyone is just a faceless name, it's a lot easier to stop treating people as human beings with an entire ethos that drives their opinions and interactions.
I think whenever you start using terms like "conservative" or "liberal" as disparagements, like /r/politics or Fox News, respectively, you've immediately fallen so far into an echo chamber that you'll have a hard time having any kind of reasonable discussion with anyone.
It's really funny to watch vaccine "debates" on Reddit. You often see two incredibly hyperbolic sides: "vaccines are giving everyone autism and don't even work" and "vaccines are perfect and anyone who can't or won't be vaccinated with everything should be killed", and both sides play with "you're either with us or against us". Of course, there's a bit of selection bias here. People who don't really care much about the issue won't speak up, so the passionate far fringes end up being a vocal minority, but that's just how these arguments go.