Yes
Downvote button next to the upvote one that cannot go below 0 rshares (hide content)
List top votes with downvotes at the bottom. (less visible)
We could extract some very valuable curation from the few downvotes that may occur.
It won't affect the reward distribution or "people exploit the rewards pool" until there are cheaper downvotes implemented in the form of a separate downvote pool that doesn't take from your upvoting power.
RE: Poll: Flags or Downvotes?