What I'm saying is society's opinion doesn't affect the reality, such as whether hitting someone has negative effects or not. Just like society believing Earth is the center of the Universe doesn't make it so, the society believing that hitting a child has no negative effects doesn't make it so.
And spanking, of course, is coercion, pretty much by definition. The very idea is: "He will be afraid of being spanked for doing something, so he won't be doing that." What is coercion, if not this? Again, it doesn't matter what the society thinks about it, it is just how language works.