This may stir up strong feelings and contrary responses, but we shouldn't write these people off so quickly as deranged madmen who unjustifiably hate the West.
Consider that since the invasion of Iraq by the USA in 2003 to topple Saddam Hussein, there have been nearly 150,000 civilian casualties.
Source:
https://www.iraqbodycount.org/
If you had an invading, occupying force, through collateral damage, kill that many people in your homeland, how much hatred would get stirred up in your heart?
Factor in then, all the ideological differences, especially religious differences, and you have a group of people that feel no moral compunction at all in killing their enemies.
Is it justified? Not at all. But is it understandable? Through their p.o.v., I think yes, very much so.