Yes all votes are stake-weighted. Payouts won't go negative, just zero in the least,which is the same as a facebook post. Reputation points are a different matter though, it can go negative. But only if flagged by a high rep account. 

Over time, I'm getting more and more convinced that curating accounts are way better than curating pure content. But that means one has to observe an account's activities over time to establish trust, which usually leads to autovoting to support. But of course, the trust can also be broken. Good thing content is transparent for the community to check from time to time if there's abuse.