It is always an interesting exercise these days to note which sites moderate comments and what it takes to get you banned.
I'm more inclined to allow an unrestricted free-for-all. I don't think you can automatically assume a congruence between the opinions of a commenter and a site.
Though one of the reasons that Australian blogger Andrew Bolt seriously considered switching off his comments facility was the fact that an ABC "comedy" program trawled through over 300 comments left on one of his posts to pick out three or four to use as weapons against him.
Yes, his site is moderated, but you'd think any reasonable person would firstly know that mistakes will be made and that things will slip through that shouldn't have, and that a few such comments have to be balanced against the rest.
But as this post from the Powerline blog shows, the Huffington Post is more than happy to ban people it doesn't agree with, which makes the continued presence of people who make the most outrageously prejudiced and bigoted remarks about Jews all the more significant.
Full post here