I have heard a trauma expert talk about how children may see spanking(the adult is bigger, towering over the child, terrifying and imposing figure) essentially they are quite an imposing, scary image of a person(this is largely out of the control of the child) and they are charged with keeping the child safe(yet show them what registers as "when we are upset we hit").
When it is done seperate of discussion where the child is helped to problem solve(not just in a control based manner) but one that helps the child fully understand how they may move forward with the root issue behind the slip up, it doesn't actually count as discipline(effective discipline helps work through root issues not just behavior in a meaningful way).
If we just expect obedience, and cut those parts out then we as
adults are not then helping them develop their critical thinking/logic(which comes from those problem solving talks as well).
As well as rremoving the bonding component of authenticity, vs control(control and authenticity are opposites).
Not to mention we don't know if they mean, spanking or abuse(the distinction is unclear there as well)- in the sense that their parents may be calling it spanking, it could cross over into abuse or what reads as abuse(if someone is stomping around angrily, doing so while angry, and having angry/aggressive body language), their way of treating the house when they go to do this or when upset, their motive, body language, how hard/much(self control), if objects were used.(etc). If their parents had a condition that has unique expressions of anger, like a rage disorder, substance use, unmanaged bipolar(bipolar rage), ASPD, projecting traumas unto the child during these times(just some examples).
Consider that you don't know what you don't know and they don't choose what they may have percieved subconciously.
I am not judging people who spank, but parents excusing certain things, by **calling it spanking**, wouldn't new, I'm afraid and there are distinctions that *can make it harmful*, and there's a line to toe(so if someone isn't meeting the developmental needs of the child, skipping important components, going about it when they themselves are dysregulated, then the fact that it *can be terrifying to a child*, comes into play(led alone the additional factors that could be present).