In fact the solution is to require solving a captcha on any post, comment or even upvotes, that would stop bots in their tracks. But is anyone willing to do this? You see, most of us (including me, I have a daily upvote from a bot which is the only sure vote I have, I would lose this if a captcha is used) depend on bots, and if there are bots the abuse will continue. Apart from this I don't think there is a practical solution to this problem