I am no mental health professional either. To me it seems Gage is totally obsessed with the 9/11 thing. He made a wrong decision in 2006, when he decided to give credit to Griffin when hearing him talk on the radio. Gage is gullible. He took the wrong path and went far too long. He can't see himself being wrong about this.
He's gone far enough to lose much of what he had. Because he is obsessed with something he sees very important. When you're that deep in dirt, it doesn't matter if one Mark Roberts tells him that he can't have both thermite and explosives. He just thinks he's found something very suspicious and important, and you are only out there to discredit him. They lose all reasoning and critical thinking skills.
I've discussed 9/11 with a Finnish man, who is a strong Griffin supporter (This man also introduced R.Mackey's paper to Griffin, and is also going to be featured in the upcoming Griffin book about WTC 7). This man can't admit almost any mistakes! He's even incredibly stubborn about the Ted Olson lying about the phone calls issue! Thus far I've gotten him to admit one single mistake, being that there weren't 67 intercepts in the year preceding 9/11. Yet, this guy seems totally sane, if not cornered about these issues.
It is a very strange phenomenon, when people become very obsessed by conspiracy theories and 9/11 being and inside job. People who otherwise seem quite sane, can believe in absolute nonsense very furiously, and are not able to see any flaws in their critical thinking. These people think I am the one, who's not critical. They think THEY are the sceptics. Their thinking is very wrong, yet they can't see it and even refuse to consider it.
I don't know, when that obsession becomes something that can be called illness. Maybe it's not for me to decide anyway