Unforgivable Curses it says it in the name they are unforgivable and the use of anyone of these curses will give you a one way ticket to Azkaban. Which is why I'm sure that students wouldn't just run around yelling "Imperio!" Manipulating  people and not get punished. Seriously the amount of fan fics I've read where literal first years are torturing people willy nilly. And you're telling me Dumbledore is ok with this? The only time I think people would use the unforgivable curses us when Voldemort had control of Hogwarts and most of the time when people have students using the curses Voldemort isn't in control of the school.