If you make down voting cheaper you will have even more down-vote-trolls than now! If anything make it cost more to down vote someones content. A lot of people have different OP as to what should be down voted. There are currently some very high profile trolls with large stakes down voting a lot of content already.
P.S. @ned

• give me 2 million warrants to buy steem tokens at or above the current market price and I will help moon steem. You lose nothing since the warrants have no initial value. I will even pay the legal fees to draw up the contract if you are willing to accept outside legal docs.