Short version: If I knew how to build a version of Tor that could be used only for Good and never for Evil, I surely would. But I have no idea how to do that well, and I don't think anybody else does either. (There are proposed solutions to do that. They are bad.)
Ahh. When you put it that way, there is a simple solution. Remember, the IP specs define a "malicious" bit that all bad, evil data packets will set if they are standard compliant. So, as long as these evil users comply with the standards, Tor can filter them out. All done :-).
