All of the above. What differentiates spanking from slapping or any of the others? It’s just a more normalized form of the same abuse. It’s been literally proven by psychologists multiple times to be harmful to the children’s development. But hell it shouldn’t even need a study to be obviously wrong.
Probably whether it’s done in anger or not. Spanking isn’t abuse, unless it’s taken too far. As somebody whose parents used it, don’t really think it affected me that much; can’t think of a time it happened where I didn’t deserve it. That said, anything can be abused, and ofc other forms of hitting are certainly abusive. But the idea that a simple smack on the butt causes great harm to the child doesn’t make sense to me