To paraphrase the master: Jim Butcher
"Sometimes they (his beta readers) will make a comment that makes me really mad, but usually as I'm flying off the handle a voice in my head says "You know your only this mad because they're right." "
He went on to say he doesn't understand why anyone would volunteer to be abused by a writer.
My point in all this is, usually the criticism that hurts the most, are the ones we feel are valid. How to fix that? Apply it to your writing, and regain your confidence through self improvement... NOT through threatening the guy who pointed out your weakness.