I find fundamentalism in its most all-purpose form, is subject
   to a form of demonic possession / mental illness factor: "strict
   adherence to the basic principles of any subject or discipline."
   Now and again, it's fine to go "back to basics". But when people
   KEEP going back to basics over and over and over again...
   structure their way of thinking around back-to-basics... no
   wiggle room... no room for concessions to... I dunno, realities
   that don't fit into the schema... ...it's a form of mental
   illness. I hold this candle of criticism to not only religious
   fundamentalism but to any. It comes down to taking "by the book"
   (or "sticking to definitions" - or "sticking to the glossary" -
   whatever - too far... and not taking a moment and going: "Ok,
   now that we've done THAT: Let's look at the real world for a
   minute. What are we missing here?" ==== I'll give an example:
   Did you ever talk to somebody who was obsessed with The Rules?
   Let's say you're kids playing a game. You're having fun. But one
   of the members always insists on stopping EVERYTHING and having
   a fit because a rule was broken? Or everybody agrees to change
   the rules into house rules but that person won't? They leave
   with folded arms because they're not playing it right? Or
   somebody who is obsessed with Logic and rules their life by it,
   no matter what the consequences or how much it differs from
   visible reality? Or a person who has a few favorite people
   they're always quoting as authorities but rarely seems to have a
   free thought of their own? [academia unfortunately trains us to
   do that.. .but I see a lot of academia as a form of
   institutionalized mental illness but I digress....] I mean,
   there's borderline. There's nerds/geeks that are just
   particular. They know a lot (I'm one of them - know-it-all type)
   and love pointing things out because they think it's
   interesting. I think that's a little different. Likely still in
   the spectrum I'm sure... but that's probably more on the
   autistic-scale. Even look at people who commit acts of
   terrorism, to get back to the OP. How many ACTUALLY willingly
   let themselves die compared to the size of their militias? A few
   guys here and there. Look how much training is required in the
   various world militaries until they reach a point where they're
   willing to die for a "greater cause"? It takes a lot. Even
   within militias, there's few that go forward with guns-blazing
   and those that do... well... yeah. We've all known ppl like
   that, whether with guns or whatever. So, yeah. Whether a
   non-moving rule-follower who continually returns to the book
   without diversion, or the guns-blazing "fuck it all" type... it
   amounts to the same thing to me: Mental illness.