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problem is that 100 witnesses cant check that volume of rewards, it's not even close to feasible. As it is, they don't even have to check steem most of the time, just keep their node running. I do agree that there has to be some kind of moderation, whether by witnesses or something similar, but it would have to be at the user level (i.e., reporting users for abusive behavior to have them banned/punished or whatever) instead of at the post/comment level.

or double the witnesses and have a second layer of witnesses for large rewards