Their reasoning makes no difference. They could be doing it because they just want to kill people, they could be doing it because they hate us, they could be doing it because they are just deranged. They are still killing people for no reason.
The reasoning does make a difference.
How do you know terrorists do not know any better?
What if I'm grown into a family, who are a part of 'Al-Khaeda', and I am taught to kill people, and told that these people hurt us, and we are getting revenge.
If they hate us an alternative was to not talk to us, or have anything to do with us.
If a bully at school, was making you give him your lunch money everyday, you could choose to just let it happen.
If they are deranged they could get medical help. There is an answer to everything, and it doesn't involve genocide.
Definitely, because if I live in a warzone, with little if any medical treatment to begin my life with, I can just call up a doctor.
The point being, the majority of terrorists reside in a location where they cannot seek help, if they are indeed, deranged.
If you are backing up that torture is wrong because they have their reasons, then I would say you are a terrorist.
I`m saying that we do not know. You or I, are not in a position to be saying why terrorists kill others. Only they know.
Edit: Are you also saying their "duty" is to kill people?
Back to my first response,what if I`m brought up as a child, and told the point of my life is to kill others.
Then I would indeed, entitle it `my duty` or `my purpose`.