That often happens regardless. You might as well spare the poor teacher from dealing with them so they can focus on kids that are still redeemable, because otherwise, if you force them, the teachers will just choose to leave the system entirely, only because you had misplaced empathy for the irredeemable bottom % of society, when you weren't the one actually having to deal with that problem you want fixed. It's easy to write cheques you don't have to cash but most people, just like you and me, have limits to the amount of abuse they will take at work, even for humanitarian jobs like nurses and teachers.