If you think that crosses the line, then you just gave anyone with access to a small botnet (or who knows how to cleverly use Tor) an easy, cheap way to cut off the income of people who rely on AdSense. And there are a LOT of those.
Outright, criminal fraud is one thing, but I would argue that it's unethical to hold up the funds he has already accrued. Sure, cut him off, but perhaps it's not the best idea to rely on the good intentions of people when you offer cash for clicks.