As much as I like Reddit, it isn't a great place for having deep and reasonable conversations about anything nuanced. I largely attributed it to the upvote/downvote system and the pseudonymity, but it's probably as much to do with the moderation and the culture of the site. I do think it's a matter of identity and culture - people aren't there to learn to challenge their beliefs and learn new perspectives and discuss things. It's too easy to go from a post about some white trash pulling a gun on protestors where people are just blindly piling on the issue to a post about whether I should dump my boyfriend because he forgot to pick me up to a post about cute puppies. Compare that to something like SSC or LessWrong (even if it isn't perfect), where everybody knows why they're there and there are significant efforts both from the community and the moderators to uphold that.