reddit's failure to attract different types of people is largely because of the way they use default subreddits. Facebook and Twitter start users off with a blank page and ask about their interests first, and thus, both platforms attract all types of people. When your average person goes to reddit.com and see anti-religious stuff or pro-some-political-candidate first thing, they assume that it's not the place for them and move on without understanding that the experience can be customized by subscribing to specific subreddits, etc.