In isolation, I would agree with you - and I might agree anyways.
However, remember that school discipline is not in isolation. Many kids are brutally beaten by out of control classmates. An occasional teacher hitting a student may stop some of that. And if they were allowed to smack a kid regularly, then it might never reach the breaking point...
As we are not discussing this issue generally speaking, but are looking at a particular incident where a teacher fractured a student’s skull, you comments would not appear to apply. The severity of this case is the issue. I can agree that teachers need to be able to apply some form of discipline that works. This was not it.