I agree there should be some mechanism to fight plagiarism I just don't see a solution better than the current system. One option is tocentralize things and put some actual steemit employed admins on to enforce some set of rules everyone has to follow.
If you don't want that centralization of power then you leave it up to the people to police themselves. When you do that people are free to use their voting power to upvote or downvote whatever they see fit, regardless of reason.