I imagine the idea is that this system should eventually lead to ads that the community actually likes - but I'll admit that doesn't seem to be happening. However, I think that most ads that reddit rages about are pretty terribe ads. For example, a recent ad for a movie (Apollo 18) was hated on because clicking on it sent you to a Facebook login page. That's no good since many people now can't learn about this movie through the ad without signing up for a different website.

Another example: I think there was a recent Microsoft ad that took you an unrelated webpage. Again, that ad is no good.

The community comments on these things because there have been a lot of terrible ads - ads that don't even let users learn about the product being advertised. However, it doesn't seem like this is actually leading to better ads...