Changing the subject
On a post about the latest right-wing outrage or stupidity: "Yes, but a liberal once did something bad or stupid, so let's talk about that instead."
On a post about the evils of Islam: "I think it's more important to attack Christianity, so you should write about that instead of what you actually wrote about."
On a post about death threats against a guy who desecrated a communion wafer: "As a Catholic I'm offended by the desecration, so lets discuss that instead of the issue of the death threats."
Each of these represents one or more actual comments I've gotten on actual posts on this blog; other readers didn't see them because of the comment moderation (well, I let the communion wafer one through because it wasn't quite so blatant a change of subject; that thread is here).
Look -- blog posts are about what they're about. If there's some other issue you think is more worthy of discussion, you're free to discuss it on your own blog. Don't go out and try to sort of police what everyone else is saying.