I disagree, Bobad, to the extent you single out Islam.    There are extremist groups or individuals who subscribe to any major religion who justify murder based on religious doctrine. Same can be said for some extreme political ideologies.

We have ample evidence of murderous religious extremism historically in the USA, from the killing of doctors who perform abortions, bombings and arson of abortion clinics, lynchings, bombings, and shootings at churches, mosques, and synagogues.

No particular religion is exempt. And that is not a slam at religion. If religion had never been invented there would be other social institutions that would serve as justification for the extreme actions of some individuals, human nature being what it is.