I like the your post regarding downvote link given in above comment.
But i again say that you can think it other way. Make a committee of respected users elected by community and equipped with sufficient SP to flag the post those are abusing (milking/farming purposes) the system. Not for as you mentioned.
Keep the one voting power for upvote/downvote and if any steemians feels that someone is abusing the system then inform to committee and committee analysis and take decision and according to decision they can downvote that user posts/comments.
Think it other way. Why everyone downvote, when we can have a committee for it.
In your suggestion first everyone downvotes others and then committee will correct. It means first we do wrong thing then we correct.
In my suggestion in first time we do correct thing.