I offer a comment system on this blog to allow people to discuss the blog post and if needs be continue the discussion on their own blog, which is what trackback is about.
I don't have a comment system for you to advertise your blog and will delete any unknown person dropping a link without a second thought.
People who leave genuine comments are rewarded with a dofollow link. Although I am thinking of getting rid of it as it's way to risky and when comments are heavy I don't want to have to keep checking if that link is going to a bad neighbourhood.
Comments are about conversation. Most people do not have a problem with this concept. It's not like this is a directory.
It might be useful if I posted a "what's acceptable" for comments, but I expected it not to get abused too much.
So if your comment does not make it through the gates you know why.
I advise everyone to be careful when letting people comment with dofollow links.