(Warning- LONG post...)
Sometimes a person deserves criticism. You need to tell a person when and what (s)he did wrong. When I missed the beat playing the piano, I would be told "no!" That in itself is a form of criticism. Not all criticism is bad; there are rules in life. A teacher who grades a child's paper is a "critic" in her own right, and if a paragraph does not fit, she must circle it and explain why. That is a form of criticism. A person who gets a parking ticket deserves it (usually), and is being criticized for his/her laziness. But reward is equally important. Never criticizing could have bad results too.
Maybe we mean different things when we use the word criticism? If you mean criticism as "insulting a child with a loud voice," I understand, but that is not MY definition of criticism; that is my definition of "belittling."
For me, criticism is "judging the merits of someone via some established standard." That is not necessarily the same thing as belittling. If a child breaks the norms, (well, adults do to), then explain what has been done wrong, and then explain what has to be done right.
A judge and jury who finds someone guilty of a crime is being critical of that person's behavior. A parent who scolds a child for breaking a flower vase is also being critical. No parent is going to react gently and take it in stride when the child breaks the flower vase, no matter how accidental. The child still broke a norm; Flower vases are not to be broken. Saying "watch what you're doing!" is a form of light criticism in itself, for me, anyway. Criticism and belittling are two different things.
Criticism can start as something good, but turn into belittling. I think this often happens. You start explaining to a person what he did wrong (criticism). After that you link it to something else he did wrong. And then something else he did wrong, till you wind up hurling insults. That's not criticism to me. That is belittling (or being a total asshole, if you want to use common speech).