The problem with the flag is that perceptions of what 'flags' are, has already been ingrained in peoples internet language. It would seem to me that putting a downvote button next to the upvote button takes away the 'flagging' idea and then it would be similar to a reddit style voting system (which is a language that people are quite familiar with). If the frontend stopped making the voter identifications public, that would avoid people impulsively going on a revenge spree. I'm assuming there are issues with this because of the blockchain being publically accessible, but at least make people work to find out who downvotes them. I'm sure some third party website would jump at the opportunity to provide that service.