If corporal punishment is effective then we don’t have to terminate anyone’s education. For some kids it may just take one painful lesson to turn them around so why forgo that and ruin their lives?

Certainly, if they also don’t care about physical punishment then expel them as a hopeless case but don’t do it reflexively as a cop out.

Two problems:

1) school education is mandatory until 16-18 in most countries, so what do you do with them once they get expelled. They have to be in education somewhere - so do you just put them in one school for all the expelled students, which is just constantly on fire? You made the problem much worse for yourself(as in - the state).

2) " there’s no benefit to keeping them in school and massive consequences for the good kids" - the massive consequences for kicking them out and not dealing with the problem are then on us, the society, because you get dysfunctional kids that got no help and just got kicked out instead. What kind of adults do you think they will grow into? Or is the answer "I don't care"?

You expel them and they become another person's problem. I heard recently of a local problem child aged seven. He's already been expelled from a private school but has entered a state school where he seriously injured another pupil and attempted to strangle one of the teachers.

Expulsion isn't going to reform them, it will just move it on elsewhere.

The moment you abandon any attempt to correct the behavior you guarantee they are “lost” to society.