Of course, reddit can happily decide to be a beacon for upholding free speech rights and can chose to allow distasteful subreddits. I am not going to argue with their right to do it.
But at the same time I don't wish to be associated in any way with that type of content.
EDIT: As there has been quite a strong reaction to me saying that I decided to delete my reddit account, I think it's worth me emphasizing what I said above about reddit being free to do as they please. I am NOT telling them how to run their site; I am merely stepping away from a community that has content that I dislike.
EDIT: I think the fundamental schism is that reddit sees itself as a collection of independent web sites (subreddits); the rest of the world is likely to see it as one place. A similar thing can be said about 4chan.org. If you ignore /b/ there's other interesting content, but in the public's imagination 4chan is /b/.