Personally, I would never EVER spank my daughter.
I may swat her hand if she tries to stick it in the electrical socket, or run over the road, but that's it.
Why? I have a broken tooth, split lip, broken eye socket, etc, all from my Adad's 'spare the rod' kick.
Really, Where is the line?
I don't see one. Physical violence against your child is never okay, unless it's to spare them that second from something worse.
I don't really see what adoption has to do with it, It all depends entirely on the child. Some children that have come from abusive homes should never be spanked, no matter how bad their behaviour is.
Other than that, it's really a matter of preference. I think there are better ways to deal with things than hitting a child.
Kap.... Now i don't even want to trust you with a goldfish.
You really have no idea, and I hope you god you don't have children for a long time.