I agree with you but ethics and profits don't go together. Expecting bots to refuse payment for upvoting bad posts ain't happening any time soon.
I use bots too but only for post that I consider worthy for more attention. Does that make me unethical? Who can judge that?
I prefer to report all abusers to @steemcleaners. I am rewarded every week for it too for being such a caring steemian.
It would make it difficult and time consuming for bots to inspect the quality of every post. What is possible is that authors can apply for membership to particular groups that utilise bots. This membership will involve demonstrating the quality of an author's existing work to gain membership. There would be some complexities around doing this as well but it's a lot more practical than expecting a bot to investigate every post that is bid for.