Violence isn't necessary 99% of the time, but the fact that it's available that last 1% is why it isn't necessary the other 99%. Some people are absolutely willing to exploit kindness, spurn obligations, and break contracts, if they can.

The fact that there exists a system of consequences backed by violence is what makes people follow social rules. Maybe the community's punishment for vandalism is a fine, or some kind of public service; I'm only willing to pay that penalty because of the threat of state violence being used against me if I don't. I'm all for minimizing the use of violence to enforce social mores as much as possible, but if it's not available at all, we start running into problems enforcing the milder, non-violent social consequences which we strive to use 99% of the time.

If someone attacks someone else and is sent to rehabilitative counseling, how do we make sure they go? In order to enforce the humane response, a violent response needs to exist as a backup.

I’m fairly sure there will remain sufficient coercive threat of human violence to keep society existing and operating well even without a state.