I support self-upvote 100%. I have upvoted all of my posts.
The issue with selling vote is the same as the issue with self-upvote and non-linear reward would also take care of this.
Linear reward curve incentivize selling votes at the expense of everyone else who doesn't sell votes. In the long run, it will lead to everyone wanting to sell their votes.
People just don't realize and don't understand how Steem works for the most part. The sooner the solution will be implemented the better.