Even isolated within subreddits, it's hard to get someone who is at odds with the ideas of most of reddit's userbase to visit a friendly subreddit when they visit the main page and see a bunch of f-bombs, nsfw links, militant atheist and liberal content, etc. My parents, for instance, would be offended by something on the main page at almost any time you captured it. Things are better now that /r/atheism is off the front page, but it's still not good.
Reddit changes its logo site-wide to celebrate same-sex marriage victories. Any time the Salvation Army is mentioned on reddit 100 redditors jump to write about how the Salvation Army opposes pornography so nobody should ever donate to them. And so on.