Now we know that there's no way to ignore the fact that a good third of humanity feel shut out of the global economy. That doesn't make them all threats. What it does mean is that if you're going to be serious about this trans-national terrorism issue, you're going to have to confront the reality of that one third. If you want to attack terrorists by shrinking their area of operations, in a classic military way, to reduce their ability to move around and squeeze them out of existence, then you have to integrate the rest of the world that remains left out.
I can't say that I have studied his theory in depth, nor that I have read any counter arguments. But my first impression at the gut and intuition check level is that Dr. Barnett has put his finger right on it.
Update: An older Michael Borone critique.