Dinesh D'Souza, Author of What's So Great About Christianity, powerfully points out that we only attack what we are threatened by. He makes the parallel between books written against God by Richard Dawkins and Christopher Hitchens, and the absence of books written against unicorns. Dawkins wrote The God Delusion, and Hitchens wrote God Is Not Great. No one writes books like: The Unicorn Delusion, or Unicorns Are Not Great, because unicorns are irrelevant. The point he is making is that there is something about God that threatens Dawkins and Hitchens. As Pastor Steve Pixler points out: the reason they are so vocal is they are "trying to drown out the voice of God in their own minds."
Inherent to criticism is a respect or fear of the person criticized. We are afraid of their influence, so we criticize in order to marginalize. Criticism is a recognition of the gifts, talents, skills, intellect and influence of another person. So, to preserve my influence I have to destroy their influence.
I write this as a confession of my own motivation for criticism. I can't think of a time that I have criticized a person that it was not born out of pride and jealousy. I have had to repent more than once of this awful sin.
Really criticism is a compliment and a display of respect, and maybe in some twisted way a form of flattery. So, when your are criticized, feel flattered and take it as a compliment. Not only is criticism the overlooked compliment, it is usually the uncomfortable and unsolicited compliment. One could say, "With compliments like that, who needs criticism?"
P.S. This is only one aspect of criticism. The subject of criticism is much more dynamic than this.