Google Ads

Is there some kind of rule that Google ads have to represent the opposite of whatever you're posting about? I post against creationism; pro-creationism ads appear. I post for the War On Terror; anti-war ads appear. And it's not just me. Tim Blair at least gets curvaceous animal rights activists in his big, colorful blog ads, owing to his high traffic, no doubt. No wonder no one makes any money off of the things.