I was born early 80s, and I'm bearing some small grudges against my parents about certain times I was smacked, especially if it was for something I didn't know was wrong, and one of the worst spankings I received from them was when I had hit my brother in a disagreement. Where did I get the idea that a disagreement could be ended by hitting? Also, smacking basically meant that my parents could instantly end a disagreement and make me cry, and it made me terrified of confrontation. I'm also still angry about a time I bumped into a blind man when out walking, when he stopped unexpectedly. My mum carefully explained why I shouldn't have bumped into him, and then smacked me. I was old enough to understand the explanation: the smacking was completely unnecessary, and only made sure I was crying and afraid. My reason for being angry is that as a teenager and young adult, it made me afraid to do things in case they were wrong: I had to have everything I did "validated" by an adult, and sometimes I think I could have achieved more if it wasn't for this fear of confrontation. In spite of that, I remember firmly arguing against smacking when I was nine years old, and I discovered a book on my parents' shelves arguing against smacking (which I still have). In the first chapter, it said "many parents regard 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 of children, listing about twenty synonyms, showing how entrenched it was in our culture.
I have heard a lot about my parents' own upbringings: they grew up in the 1950s, their parents were born about 1910 (there are big generation gaps in my family), and they did what they believed was right at the time, and they were certainly both smacked as children. I later found out that my dad's family was full of conflict, making him very angry, and he himself said he only mellowed of this after twenty of thirty years of being married to my mum. However, they were liberal in many other ways, and I was shocked to find out about "stricter" families. I do have a very loving relationship with them, and while I will not forget smacking, it was only a small part of my relationship with them. We don't usually discuss it, but I have sometimes imagined myself saying to them very clearly "you will not smack my children, or even joke about it", but I've not actually said this, because I don't have children.
Even Tony Blair admitted to smacking his own children, when it was debated: not making it right, but it was still "accepted" even in the mid 90s, although not so many parents did it then.