Yes the spam and plagiarizing is the issue I worry about. Blurt has no downvotes, I wonder how they will deal with that when the time comes.
Steem had a huge spam problem that was largely taken care of via downvoting at the time.
I agree that downvotes right now are being misused though.
RE: The Hive Whitepaper and updating the DPoS protocols for downvoting with a community proposal.