I used to think it's ok. We were smacked (or threatened with it at least).
Then I thought, no, I don't like it, but 'each to their own'.
Now I just think, no, it's not ok. It's not ok to use violence to solve problems. Nor is it ok to physically dominate people like this. It's not ok for adults to hit other adults, so why would it be ok to hit children? Doesn't make sense to me.
Plus of course children learn how to treat us and other people from the way we treat them.

I'm not pretending to be perfect or anything - I've done things I think are unacceptable - but I'm working on that and I'm not going to pretend it's ok.