> We have a lot of data showing the corporal punishment has negative effects on children, on average across the population.

I think the problem is that "corporal punishment" as a term is just too broad. You just used it upthread as "getting a spank" which is relatively minor.

The studies I am aware of showing negative effects use the term to mean "regular and systemic caning".

Those are two very different things; the studies are not studying the thing you referred to.