a really good reason not to spank kids isn't even that it'll traumatize them, but it'll teach them, at an age where they're still absorbing the implicit rules of society, that the correct remedy for wrongdoing is an equal and opposite amount of pain.
in this lens there can be questions of proportionality--how much suffering is justified for a particular offense--but the answer can't be "none" unless you think the offense was actually a good thing. inflicting suffering is our means of expressing disapproval. often it is the only means considered sincere.
(and I have not been immune to this. I'm still not. it feels knee-jerk good to pay evil unto evil, especially in a world where that's often the only option available besides "pretend it didn't happen.")
for a while I held the position that spanking isn't that big a deal as long as you dispense it according to predictable rules and not in anger. I do still think it's relatively less harmful to make it about The Rules instead of directly about your feelings. but... isn't it still kinda fucked up to write "the way we will fix this problem is by hurting your butt" into your house rules?
even for time-outs, I think there's a difference between "this is to interrupt the behavior and let you cool off" vs. "it's not fun having to stand in the corner, is it?" that's extremely important.
this isn't actually parenting advice. what it really is, is a scream of exasperation at the way so many adults talk about problems in terms of "looks like somebody, somewhere, needs to be suffer more! let's fix crime by spanking criminals harder. let's fix war by spanking our enemies harder. let's fix the economy by spanking people for not working. let's fix healthcare by spanking people who don't have Healthy Habits. I am a hammer and punishment is my only nail. I am a very serious practical thinker."
and, I don't know, maybe they'd be less like this if they were raised with a mentality of "when you cause a problem, you have to work hard to fix it" instead of "when you cause a problem, you deserve to be hurt."

