Sitting in an assigned seat is hardly "punishment." It is an efficient and reasonable attempt to impose discipline.
Suppose you have a cafeteria with 200 kids and no assigned seating. Everyone gets to sit with their friends. 10 kids misbehave on a regular basis. Rather than punishing the 10, the school changes the policy to assigned seating at lunch. Now, 190 kids who weren't doing anything wrong are now no longer able to sit with their friends during lunch.
I find that neither efficient nor reasonable.