Yes people can get set up but there are true bad eggs such as those who think summoning demons is a good idea.
Right, though I think I remember Dorian mentioning that the magisters in power practice blood magic and all that bad stuff, just they do it in private. Obviously doesn't mean they're all summoning demons, but I highly doubt that it never happens.
Anyway, I don't think a system with mages in control is a great idea, though I wouldn't be opposed to a system where mages -can- be in control. Hmm, I wonder.