As I said, Steem is based on most stakeholders voting in the network's interest (which if the system is properly designed will also be in their personal interest). If this is true, then most of the time when a downvote is not deserved people will come together to counter it with upvotes. If that's what generally happens and if when it happens the downvoter suffers a penalty then continued abusive downvoting becomes much less likely. If most of the stakeholders are malicious and will downvote good content just to watch the world burn, no protocol change will save the network.

The change I propose would make downvoting less useful for rewards disagreement, but I see that as a much less serious issue than outright abuse. It's imperfect, but I still think it would be an improvement.