I think it has more to do with shitty lives embracing death, especially when death = paradise. And since martyrdom pays best, any enemy will do.
Too simple?
It has a lot to do with where you were born. It started with Christians battling Muslims for control of Jerusalem. Christians for the most part have evolved from killing in the name of god, but the Muslims still think its the Richard the Lionheart, led west.
Like someone stated earlier. There is no reasoning with radical Islamists. They literally believe that they are doing god's will.
I'm sure many people in the middle east view America's invasions as terrorists acts. We just like to pretend that it's only our viewpoints and opinions that matter on this subject.
The reason why many Muslims cheer this on, is because they treat their "religious fighters" like the west treats it's veterans and active military.
Do you think they liked it when we celebrate the death of Bin Laden, or the death of a high-ranking Taliban member, during a drone strike?
Two different ideologies.