My point is not just that it doesn't work, but it's actively counter-productive. It makes your children mind you less, not more. Why? Because it reduces your bond with them, reduces their trust for you, and reduces your ability to role-model. These are your three strongest parenting tools. Why would you want to reduce them?
Obviously, if you're trying to teach your kids not to hit, then hitting them not only is not an effective way to do it, it does just the opposite. Teach your kids to hit others--spank them.
Your options are not: spanking or "soft warnings/approaches." Your mother had many other options available to her. She could make your life plenty miserable without spanking you.
O.K., for example, this morning, my kid wanted ramen in her lunch, and wanted to cook it herself. I let her start. She argued with me when I told her how, so I said I would do it. She argued with me about that, so now she doesn't have ramen in her lunch. She got it together and apologized enough to get breakfast, which was next on the list. I could have spanked her, but I didn't need to. As usual, I, the parent, have all the marbles. It's my stove, my ramen, and my breakfast. My way, she sees that if she wants her way, she has to cooperate, which is a good lesson.
Had I spanked her, it would tend to make her rebel, not want to cooperate with me, and, worst of all, undermine her desire to bond with me and emulate me.
You keep saying that science assumes always, 100%, absolute, every person etc. It doesn't. We just get general tendencies, such as that in general, spanking will tend to reduce IQ and increase criminality. So, again, why do it?
You may or may not have had a higher IQ had you not been spanked, we don't know. (WHy would that offend you???) We know it doesn't help, and in 1000 kids, will tend to have that effect.
Since it makes parenting harder, and has negative effects, why do it?