In his groundbreaking "New Atheist" best seller, The End of Faith, Sam Harris persuasively argued that the most dangerous thing on earth is a True Believer in an Eschatology to be desired. He used the Islamic faith as particularly odious and repugnant to common human values and rights, citing to the many passages in the Koran about killing infidels and other 8th century notions of tribalism. The reason some Americans are joining ISIS (ISIL) is that suicide by cop in the U.S. is a lot less exciting. Since birth, they've been taught that a superstitious big guy in the sky is looking out for them and has an afterlife at the ready. Those converted from Christianity are abandoning a God who sent himself in the form of a Sun -- in fact, the Invincible Sun (check your forecast). This Krishna Sun motivated the bleeding of the Mithraic Bull by which sinwashing these Son worshipers baptized the faithful and lent syncretisitic (pagan) significance to the Pauline-Constantinian religion of Reb Yeshua, made law at Nicea in the 4th century. Its protestant Dominionist evangelicals, hungry for power and significance -- the authentication of their apocalyptic beliefs in coded gospels warning of Nero Caesar, take inspiration from Rousas John Rushdoony (above), who for all practical means is their very own Profit. He inspired them to send money to Israeli conservatives for the building of more settlements in the Levant so that Jesus will put the Beast to the test, have Dominion over all the earth, and lift the faithful to Heaven in the Rupture. That people actually believe in this shit in the 21st century is just plain insane. Seems to me evangelical Dominionists are no less dangerous than the worst jihadi.
Evangelical dominionists and jihadis have one thing in common: they are both True Believers. They accept their holy books to the last chapter, verse or surah, not minding the rampant contradictions throughout those documents. They can't be bothered with analysis; they only care that their cause is RIGHT and they get to be RIGHT by associating with it.
These are the hard nuts to crack, even using Peter Boghossian's techniques. When/if they fight, they will likely fight berserk. If you want to stop them, you're stuck with killing them. Negotiating with the ground pounders is useless and their leadership won't be much better.
The Taliban - ISIS - other like them - they're cancers, for all I can tell. About all you can do with a cancer is get rid of it, whether that means cutting it out or so isolating it that it can't spread, but that's what we're stuck with.