That would lead to new people getting ignored. I was a complete noob when I joined, and not even a week after I got my first successful modding experience, I started helping people. How could have people taken me seriously when my profile had said I have done nothing? Also, our moderators are perfect, we don't need anymore, they give help to us like normal members, remove spam and garbage, and don't abuse their power.
EDIT: I've just looked around simple, and there are people with negative reps. I do not think this is what we want here, because they are doing nothing wrong in my eyes. In my opinion, without a rep system everyone here (with the exception of moderators and admins of course) are equal. I like that idea, where everybody's advice is just as powerful as another person's.