I think the topic is nuanced - because for every person who was smacked and felt abused or vulnerable, there is someone who felt ok about it.
I was smacked infrequently, usually on the leg when I wasn’t listening or was being intentionally annoying. I used to find it funny most of the time. The times it upset me I didn’t used to get upset about the smack, more the situation. It doesn’t come up in our relationship at all, and whilst I get annoyed with my parents now, it’s not about the smacking.
But it wasn’t frequent and always felt justified. I’m sure I’d feel differently if it felt cruel or was to hurt me (my mum used to do it out of desperation when nothing else worked and it wasn’t hard, was more to shock me I think).
I have another friend who was smacked and he didn’t see anything wrong with it, he feels it was a good way for his mum to set boundaries.
My husband was threatened with a slipper belt by his dad. He laughs about it now. Again, he got smacked infrequently and it doesn’t raise any negative feelings for him.
I think the family situation, how loved the children felt, how caring and rational the parents were etc plays into the response and reaction of the child. Children need to feel loved.