I believe the person you are replying to is emphasizing the "~" in your comment. Yes, it's not like half the kids will commit self harm because they are bullied, but a very small percent will. How do we, as a society, weigh their suffering against those who are being surveiled without ever having done anything to trigger it?
Teachers, students, administrators, and often parents already know who the bullies are. The question is what to do about it.
The school authority figures (teachers and administrators) both know who the bullies are, and enable/cover for them. My theory is these figures often were once the bullies themselves back when they went to school, and they identify with today's bullies. They'll watch and wait until the victim fights back, and then punish the victim using the "Zero Tolerance for fighting" excuse.
Like do you actually think any kid who was a bully you grew up with went into teaching? There definitely are a few, but just like in the kids’ case, it’s suuuuuper obvious who they are — even as adults — and they are not the majority case in any school system I’ve ever been a part of.
FWIW it is literally legally difficult to do anything. A lot of forms of bullying are not illegal per se and kids — even asshole kids — do have a right to an education.
I think it odd how many wrong applications and problematic uses of in loco parentis schools actually use, but when it's dealing with a bully, it's all of a sudden retreating behind "well, legally we can't..."