Not to mention that such sanctions end up being applied in a very selective and classist way. Try to send a kid from an affluent family to reform school, and you will have their parents, their parents' friends, the local council, and the local MP on your neck, trying to sway you. But it's "rules are rules" for the kid from the single-parent family who works 10h to make ends meet.
This affect the poor more than the rich and to not sort it out affects the learning and safety of the people with less resources.
This sounds smart, but how do you imagine tolerance in this case? Student can beat other students and teachers, but only once a week?
School is also for learning how to function in society, and this means precisely that we need to teach students consequences for their actions. Beating someone up when they are adults will not end up with just stern talking.
A zero tolerance policy doesn't even sound smart, so it's even more surprising to see people arguing for it.