I understand your point of view but find it oversimplified. A traitor is not a traitor because he/ she has a different point of view.
It's not that Zinn has a different point of view. Lots of people do. It's that Zinn supports the enemies of the United States and that he has worked professionally to undermine the United States and its values. He is a traitor.
What I can't understand is why you'd defend Zinn. Are you related to him or one of his students? Or, Heaven forefend, are you Zinn?