It's full of racists, misogynists, bigots, pedophile apologists, contrarinists, conspiracy crackpots, karma-whores, hipsters, Libertarians, college liberals, eugenicists, and all other form of scumbaggery that you might encounter on the Internet. The real offense is that there's hardly any visible dissent from people who have half a fucking brain, due to the way the upvoting system works. It's like the website is manipulating you into being an asshole with all of the civility and proper grammar of the posts. If you want to get away from that on reddit, you have to go to the non-default subreddits and those are a bit of a hassle to find out about. It's far easier for the average person to just get the fuck out of reddit altogether.
TL;DR: Reddit is (hate group who must not be named) 2.0