There is no proof of brain.  The whole system in the end is about accumulating, in Ned Scott's own words, points.  There was one an Ideal, a volitional moral standard, for not reducing it down to a purely POS system.  But the fact that it was a POS system under a fictional POB has been mocked since nearly its founding.  It's basically POS with a beneficiary option aka Proof of brain.  Even supposing there was an HF to stop self-voting, the remedy would be to start a second account and upvote it from the primary account.  So long as steem has that beneficiary option, the "problem" will not go away.  And if you remove the POB system and go purely POS, then the steem chain would reduced to complete s___posting controlled by bots.  Steem is not even a place now where you can posts things to prevent full censorship anymore-which is about the only value it had when big tech was censoring everyone-including censoring voices who were warning us about corona in it's early days, to now censoring speakers who take corona lightly.  The world is full of good and bad ideas, but Chinese controlled big tech wants to ensure only their truth is heard even if it is proven false and deadly.  often times their truth comes down to political agendas;  SJW agendas that have proven deadly and in some cases genocidal in America and Europe.

  It is what it is, and Justin sun destroyed the community and the anti-censorship utility.  Now that the community has gone to Hive, you are going to get more and more users to use the chain for things it wasn't intended for but had no real mechanism to stop-save for the whales and bots that were in place to downvote crap to save the chain to protect their investments.  The Whales who held SP are probably are in the process of moving to hive, the bots had their delegations by steemit removed.  And even if we suppose a bot was banned, another one could be created and or purchased with ease.  These are not things that can be micromanaged, and expect a big HF on its way

  In the end Justin Sun is presently using his centralized powers will just modify the front end and condensor api to prevent peoples private and frozen NFTs [their posts to steem] from ever appearing all while going on a speil about protecting property rights.  What really prevents you from selling the permlink key pair "zzan.witness"-"the-truth-of-the-ugly-witness" NFT to another user that doesn't have the same permlink (or modifying it so a user could buy multiple copies;  example adding an additional [or equivalence to an additional] db column called postowner)?  It is a feature that could have been done long time ago, but it is now Justin Sun who keeps your NFTs frozen.  But if he finds a topic or users that he finds undesirable, he'll just disappear these NFTs while he rants about protecting private property rights.  

  Many of us knew what Justin Sun would do the very moment he talked about moving to the tron platform.  The tron chain couldn't handle steem, and later it was confirmed to be over BTSF.  It is in the nature of the CCP, like big tech, to control what people can say or hear.  And now the CCP owns you as a witness.