Why is "this post deserves more reward from the pool" inherently acceptable but "this post deserves less" somehow invalid? It's a governance system, all stakeholder views are valid.
You should review my transactions more carefully before you make such a statement. If you do, you'll notice a) I am actually powering up more than I am powering down and b) my Steem Power comes primarily from buying it, not the rewards pool. ie. I'm one of the people who is with regularity funding the rewards pool with my money. Without people like me there is no rewards pool. Why should I continue to support it when my rights to decide how that money is distributed is taken away?
One is giving another is taking away from what someone else already gave you... If you don't see the difference...
We have a right to decide how our money is spent. No money is given until the voters collectively decide, downvotes are part of that. If you read the white paper, there is a whole section about why it's necessary.