What surprised me most is the guy was a Major, which is a well ranked officer and you don't go to be a major in the Army if you are not doing something right to get there in the first place. This also means he had been on the Army for a long time. This is not some new recruit down the ranks.
Usually religion, or the perversion of a religion, is used as the excuse when the individual already has a deep problem or rage going on inside.
He made his religion the issue by his many open and very direct statemens, and actions. My guess is, over time, such open, direct, and contrary statements resulted in other soldiers ostracizing him and verbally harrassing him over it. To the point that he was seeking to get out of the military over it. He was clearly disturbed, and his deployment orders pushed him over the edge.
I blame him for that, for his actions...and I blame the system that kept him in the position he was after so many warning signs over so many years. I think in their rush to get people like him into the psych positions, that they did not do a thorough enough check on him.
He atteneded the same Mosque as two of the 911 hijackers and was schooled by that same very radical Imam. That coupled with his views should have led to him not being in the position he was to counsel troops going to or returning from the war zone IMHO.
As to his rank, he was a Doctor, and one that was in much demand. After the schooling the military put him through he probably graduated as either as a full Lieutenant or a Captain.