...why are down voted post and comments greyed out?

This is not a blockchain problem. You are describing problems/solutions with a particular condenser. When I used Busy, I frequently saw posts and comments that were hidden on Steemit.com. I think a better argument to make would be a configuration setting that disabled the greying out of posts/comments. @Steempeak has been very agile in adding features, and would probably add that if there was enough interest.

I down vote for one reason and one reason only and that is plagiarism.

As I said, you can downvote based on any criteria you want. What you can't do, is dictate to other sovereign voters what their own individual criteria is. Sure, a particular condenser could force a voter into categorical downvoting if they wanted to, but I don't think that would be widely supported. I would not support that.

Your arguments seem to be an appeal for centralized governance. That kind of defeats the purpose of a blockchain. Decentralized governance can be messy at times, there's no denying that.