I'd delete if they were idiotic and not useful of for further discussion. As you say, you don't want to provide a forum. The second thing to consider, which I don't think you mentioned, is whether or not your students read your blog. There is the responsibility of a teacher to provide context and critical thinking tools to students before exposing them to "Teh Stupid".
I have used similar comment threads in class when discussing fallacies and rationality in science, and they provide great examples of people stuck in a non-scientific mode of thinking, especially as they often believe they are using science. There's nothing like good pseudoscience to illustrate the difference from real science. If, however, the comments are simply uncritically supporting pseudoscience and are confusing students, I would delete.
To those that cry censorship, or 1984, they hyperbole is a little silly. Teachers are required to censor, and would be irresponsible if they didn't. I don't allow homeopathy to dictate what's taught about the properties of water, and I certainly wouldn't allow IDiots to determine what I teach about evolution.
If you don't like it, it's not censorship. Get your own blog and say whatever you like.
Cheers,
Ron