I think - as others have said - that the part of "belief" is important in all this, in addition to the rest.
The "warrior trance" or other alterations of consciousness (such as induced by repeated, simple rythms, chants and the like) is a known fact. Add on top of that a bit of "it works" (providied by a belief system that includes such mental states as part of the 'real world') and you have it (and the occasional drug or chemical can also help).
Africa is a good example of this. It is still a land filled with mystical beliefs - that actually *work*, in a certain sense.
A mate of mine was part of the French "Licorne" operation in Ivory Coast - basically a buffer between the rebelious North and the contra-rebelious South (all political and financial interests of former Colonial powers aside). Rioters would go and see the local Marabout (not necessarily muslim BTW) and pay him for 'protection' - he'd give them herbs and chant a bit and that would make them immune to bullets.
Now, my mate would tell me : try to control an angry mob which firmly believes you can't harm them. Even firing .50 cal over their heads or at their feet simply doesn't work - because they 'know' they're immune.
And what of the occasional collateral damage ? Well, he simply dodn't believe enough, or the Marabut wasn't good enough (and would probably be lynched afterwards).
Also in Africa, you can have your penis stolen by someone barely touching you in the street - which is the cause of a lot of violent deatsh ther. That's OT, but it shows the importance and weight of belief in these cultures.
Now, there is fanaticism and fanaticism. A red, blood-hot one and a cold, intellectual one. Africans, Berserks, Amok and the like would be part of the firs, while terror plotters, SS, and the like would be part of the other. There are common factors between the two, and they are not mutually exclusive. But they're different. The first would rely more on 'natural' reactions of the Human Animal (spread on a background of cultural beliefs), while the latter would simply be born of cold Belief and indoctrination - more "intellectual", in a way.