To be fair, he didn't actually use Quire's power for personal gain. It was to help the school and therefore, the children. In that sense, it was for very selfless reasons. As far as being a teacher, with the exception of higher math and physics, he could probably teach just about anything, given the length of time he's been around. He's probably met and had drinks with quite a few ridiculously famous people. Of course, that was in those times when he wasn't a spy/mutant weapon/savage or fighting Sabretooth for the millionth time that year. For all of his short-comings (pun intended and then some) he's actually one of the best people to have as both a teacher and headmaster. He's most certainly a disciplinarian, though his attitude can sometimes be called into question, though never his motives.