Although I do now have a great relationship with my parents, certain memories of being smacked have followed me into adulthood, about which I still have strong feelings.
A book from the 1980s arguing against smacking said "many parents see it not just as a right, but their duty to hit their children". It also noted that our language has developed a remarkable vocabulary to cover hitting children, listing more than twenty synonyms for smacking, implying how entrenched the idea was. Indeed, I remember frequently seeing children being smacked in shops, in the park, anywhere. More recently (a week ago) I saw a child run out of a building, towards a road. The boy was duly swept up by his mum, who then had stern words. But in the 1980s, that child would almost certainly have been smacked, and then crying and unable to understand his mum's careful explanation that running into the road is dangerous.
The moments which I remember most were when it was for something which I didn't know was wrong, where my parents saw it as their "duty" to do it. Aged seven, I didn't expect a blind man to suddenly stop walking, and I bumped into him. My mum explained carefully why I shouldn't have bumped into him, then she smacked me. I had no intention of doing anything wrong, and there I was suddenly being made to cry in public. (That humiliation was one of the worst things about smacking, as far as I was concerned.) Meanwhile she would cheerfully use phrases such as "if I didn't, I'd be a bad mother" or "I am not in the faintest bit sorry".
Moments like that gave me huge anxiety, and I was incredibly risk-averse as a child, which I think led to other problems such as being a people-pleaser, and being unable to take initiative. It wasn't until my mid-twenties that I managed to do things "without being told". Sometimes I feel angry that I could be much more "successful" in life now if it wasn't so afraid of taking risks. As a teenager, I didn't ask for help if I needed it: instead I lied and covered things up.
At my primary school, there was never any hitting (although some of the older teachers spoke wistfully of it), but one of the worst transgressions children could commit was to do something without being told. I fell foul of this a few times, for example starting to tidy up, and then being humiliated because I was doing it without being told. This had the same effect as the blind man incident above, and secondary school was quite a shock when you're expected to take a lot of initiative.