You really can't change human nature. If the downvote feature isn't functioning in a manner that the community deems appropriate, then the feature needs to change. Educating people doesn't really help. Reddit always tried to educate people that the downvote button wasn't a disagree button, but it gets used that way regardless. You'd need a means of somehow auditing downvotes, or limiting their use, or identify who downvoted, or a means of contesting a downvote. You essentially have to discourage the behavior so it's only used when it is necessary.