Steem payouts are and have been since the white paper a consensus system. You should absolutely be allowed (by the blockchain level rules) to upvote your own posts. But others need to be allowed to counter your votes, to facilitate the end result of payouts by stakeholder consensus.
Witnesses must allow you to have your say, but other stakeholders don't have to allow you to have your way.
oh yeah. that is the only logical solution to this whole self vote thing.
if you think someone self voted more than the post is worth - flag.
otherwise who cares. you should only be judging posts by their payouts anyways.
The differences between posting and commenting would seem to suggest far different parameters of judging value- who would ever bother with flagging a comment for anything except blatant abuse?
I would flag a comment that was making more than I feel it is worth.