I upvote good/insightful points people make and downvote trolls and obviously misinformed/willfully ignorant points people make or stuff that's completely off-t

I upvote good/insightful points people make and downvote trolls and obviously misinformed/willfully ignorant points people make or stuff that's completely off-topic. Why do I do this? It's my little contribution to the community to push the garbage to the side and let the good stuff rise to the top and spur good discussion.