On the one extreme of the spectrum are those who believe simultaneously that (a) blogs should not post anything that might offend them, even if they are only visiting a given blog on a first-time fly-by and (b) that anything should be allowed in the comment threads, up to and including insulting the blog owner and his or her other commenters. I call this the "The World Exists to Serve Me" contingent.
On the other extreme are those who believe that (a) blog owners can say whatever the hell they want, however they want, and if the people visiting the blog don't like it, they can go away (common rallying cry, "No one's making you read this blog") and (b) blog owners can do whatever they want with regards to their comments threads -- ban randomly, edit comments according to their own whims, refuse to have any comments, ban people who disagree with them, etc. I call this "It's My Blog and I Can Do What I Want" crowd.
Personally, I lean more toward the latter than the former, in that I don't give a rat's what some random stranger thinks about my blog, I dislike intensely the arrogance involved in telling other people how to blog, and I see no reason to spend my money to host comments that are insulting and unhelpful, or to provide a forum for jerks.
In practice, though, I think most people who blog (and who comment) fall in the reasonable middle, trying not to be deliberately offensive in their choice of topics and writing style and word choice (or, alternately, warning people up front about what to expect at a given blog), and allowing reasonable debate to occur in their comments threads, if said debate is constructive and respectful, at least according to the culture of that particular blog.
It's that last part that gets tricky: according to the culture of that particular blog....
Lots more there. Worth a read - worth more of a read that I can give it right now, actually. But especially as someone who's been attacked not-infrequently by that former contingent, I find this interesting and worthy of exploration.