Doesn't the flag feature make downvoting superfluous and meaningless? The automatic ranking systems (Google, Flickr, etc) usually only calculate positive point

Doesn't the flag feature make downvoting superfluous and meaningless? The automatic ranking systems (Google, Flickr, etc) usually only calculate positive points, or otherwise they simply ban irrelevant/offensive content manually. You're either good or irrelevant - that's the philosophy and it's very positive in all respects.