The article points to immoral subreddits (racist, misogynist, pro-rape, etc.) Noteworthy that it's not a new problem; there have been several immoral subreddits, promoting child pornography for example, that were shuttered earlier this year.

Another problem is the group think. Certain subreddits, for example /r/worldnews, tolerate only a particular political slant. If your posts and comments contain a dissenting view, and they're downvoted off the front page and out of sight.