The fanatical Muslims hate our culture and everything we stand for. They consider people who don't share their religious beliefs "Infidels". Its the same thing with the Christians thinking everyone who doesn't believe in Jesus is going to hell except Muslims think they can save us by killing us.
Because they are "radicals" and as such can't stand the idea of people doing things they (the radicals) don't approve of. Why have "radical" Christians blown up clinics that perform abortions? Not because they are Christians, but because they are RADICALS.
It started with crusades. Question asked, then . Do you want Tobe a Christian? If answer was NO. Guess what ? Some Noble Knight cut there heads off. Sound familiar? These radical extremist only know one thing kill AMERICAN.