To suggest that non-corporal methods of discipline is the culprit and all those other things have no effect on the behavioral development of children strikes me as a bit of wishful and perhaps fetishistically motivated thinking.
Lack of CP may or may not have had an effect on the change in behavior. There is actually no was to tell as the lack of CP’s use can never be viewed outside the context of a myriad of other, perhaps more significant, variables that affect children’s behavior.
In the U.S., paddling still goes on routinely in 22 of the 50 states. One of those states that still uses the paddle is Colorado. Columbine High School is in Colorado.
Obviously the threat of the paddle and its use throughout grade school and into secondary school in Colorado had little effect on the fact that kids who could be subjected to CP came to school and murdered their classmates and teachers en masse.