The act of slapping literally is physical violence though.

So you have to either physically or emotionally abuse your child? There's no option for not doing either, and avoiding the lasting negative impacts? I don't think the existence of emotional abuse justifies hitting children. I think it is just lazy, irresponsible, or vengeful parenting. I was smacked occasionally and I don't think it did any good and, though it was rare, probably did some amount of bad.