The move away from physical discipline has led to this
BUT - not because physical discipline was good. It was just easy.
The reality of parenting, teaching, and any form of discipline is that doing it in a reasoned way is challenging. And a lot of people just can't or won't. It takes far far more consistency, thought, patience, time, effort, knowledge etc. to maintain authority through reason/compassion, rather than fear.
When done well, it is 100% the best approach. Modern non-physical authority IS better than traditional fear-based authority.
But..
Fear based authority is better than no authority.
And that is the problem. If a parent or teacher can't use fear... but isn't willing or capable of creating reasoned authority, then you end up with out of control children in families + classes.
Putting it into school contexts.
Great inspirational reason based authority > Physical fear based authority > No authority.
The problem that a lot of "older" generation do correctly identify this problem, but then conclude that we need to go back to Physical discipline.
When in reality we need far more training, time, support for parents to learn how to parent, rather than just presume everyone is capable of automatically creating reasoned authority with children. (And equally far more training, support, and resources for teachers, smaller classes, more time to prepare etc.)