1) In your profile, define what you consider to be acceptable behavior for your blog. Some people don't want vulgar language, some people don't want logical fallacies, some people don't want politics -- whatever your boundaries are, let your audience know.
2) Also state your policy for dealing with inappropriate posts: ignore, disemvowel, delete, etc.
3) If inappropriate posts create a problem on your blog, be willing to moderate. The "boot" icon appearing with this post is a popular one for moderation posts.