Because discipline can be made to stick- Timmy can be suspended and when Mom comes in to say it can't be his fault, because that would imply it was her fault and she's never been held responsible for her actions before, oh well too bad video doesn't lie. Otherwise admin backs down about 50% of the time.
If you want to point out that this doesn't help Timmy, I'd agree. It does help the other 29 kids in the class, their parents, the teacher, and admin though.
It helps the other 29 kids in the class until there are altercations involving 5-7 of those.
Then it helps the other 22 kids in the class.
What's the endgame? Do you suspend half the kids in the classroom because they're causing a disturbance for the other half?
Something this whole argument misses is that school is a great mechanism to teach kids to interact with each other and learn to solve problems.
It's a bad idea to teach kids that everything is always black and white.
If you want to point out that this doesn't help Timmy, I'd agree. It does help the other 29 kids in the class, their parents, the teacher, and admin though.