I do not believe in violence ,unless used in self defense. But I also grew up at a time when spankings were quite common (myself among the recipients of), so some time I think a little smack on the bum might be useful in curbing bad habits in young children .Not enough to injure the body but enough to hurt the ego so they know you mean business!
There's no such thing as constructive criticism. It's an oxymoron.
Yes, I believe so. It depends on how one shows their criticism if they express it in a verbal or physical way. That is my opinion.