Although I have a great relationship with my parents now, I do feel strongly about being smacked, and that even though they meant well, in some ways it has messed me up and made me into a less capable adult. I haven't forgiven them for these, and I still feel angry about them. Examples of when I think they did it "wrongly" were:
When I tried to stand my ground about something, such as my brother deliberately winding me up. Result? I became afraid to stand my ground about anything, and was a total pushover as a young adult.
When I once bumped into a blind man; he stopped walking when I didn't expect it. My mum carefully explained why I shouldn't have bumped into him, then she smacked me. I would have understood the explanation, without the smacking!
It made me afraid of being out and about, in case accidents like that happened.
I once (very lightly) hit my brother when we disagreed about something small, and I received one of the most severe childhood smackings ever. Was the irony totally lost on my parents? Did they not see where I might have got the idea of hitting someone if I disagreed with them?
If I lost or broke something, I was sometimes smacked. Result? I never owned up, and got into big spirals of lying and covering things up as a teenager and young adult, which sometimes got me into much bigger trouble.
Basically, I grew up afraid of accidentally doing something wrong, became very risk-averse, over compliant, which I think really held me back as an adult, and I might have achieved more by now if the fear of being smacked was not present. I remember that when I made a small mistake, I'd sometimes plead in a small voice "don't smack me".
I don't have children, but I've sometimes imagined telling my parents (MN style) that if they ever smacked any children of mine, it might be the last time they'd see them.