For more background on why we have the current rules and some reasons for the changes, you may also want to read an old post I made: https://steemit.com/steem/@blocktrades/voting-abuse-and-ineffective-curation-a-proposal-for-blockchain-level-change
It mostly still captures my position on the proposed changes, although I've been talked into the experiment of having a separate downvote pool (this is the one change I'm not totally comfortable with of the changes approved by the majority of witnesses, but I think it's worth testing it out).