It's the chain of causality that's causing you some problem. That's among the first things to go as you develop Alzheimers.
The causality is the same, they are and were fanatics.
Anyone that has a strong enough belief in something, right or wrong, will die for those beliefs.
I am saying that if they are martyrs and killed for their beliefs, or kill others because of their beliefs, it doesn't tell you whether those beliefs are right.
Just because a person is willing to kill or die, does not necassarily make their beliefs true, in any sense of the word.