We should really divide this discussion into two.
Do you have children? Do you believe in spanking?
If you don't have children? Do you believe in spanking?
There were A LOT of things I said I wouldn't do prior to having kids and guess what. . .I was an awesome parent pre-kids. LOL All I can say is never say never. You don't know what will or what won't work for each of YOUR kids until you're in the the throes of mommyhood.
Be careful who you judge in public too. You're seeing a situation or a family for 5 minutes, the family has been together the entire day. You don't know what happened that morning or 10 minutes ago. People don't exist in a bubble of time.
As they say, the best parents don't have kids (yet).