- The exclusivist orientation holds that all nonbelievers will be condemned to hell on judgment day. "No salvation outside the Church" was the Catholic formulation.
- The inclusivist orientation holds that God will save good people who don't share the faith, even if they don't don't know it. This is a more generous view, if condescending.
- The pluralist orientation holds that all religions represent valid ways to find sacred truth. Many paths, one mountain. This is my viewpoint, and I would include non-religious people, too. The idea is that we can all learn from each other. For me this is the necessary attitude in the 21st century.
Let's look more closely at exclusivism, since this is the attitude of the ISIL types. Exclusivism is mostly found in Christianity and Islam, which is why these religions have a greater focus on conversion than others. If you really think that the "others," the nonbelievers, are going to be punished, you have a moral obligation to try to convert them. That's why all those Catholic missionaries traveled hundreds of miles up the Amazon to find every last "savage" on the planet. They were motivated. The irony here is that if all the Christian and Muslim exclusivists got their way, each would succeed in converting the other, and they would just swap places!
Throughout history there have been true believers who see no contradiction between military action and either the propagation of religion, or at least what they perceive as the defense of it. I think such attitudes were fairly common centuries ago. It is a more recent development to think that there might be any contradiction between religion and warfare. Today, we think in terms of just and unjust wars, and most of us would not want to say a war is waged in the name of a religion. Some still do, however. A small minority, yes, but problemmatic. Some American Christians think this way. So it's not just "them."
However, even if an exclusivist is committed to nonviolence, which most are, there is still the nagging sense that they think there is simply something wrong with the other. They are suspect. I mean, if I could see the Truth and submit to it, the true believer wonders, why don't they? In essence these others are delegitimized, which means that dealing with them in constructive ways is going to be that much harder, even if the bias is so subtle as to be not even articulated or acknowledged by the true believer.
Let me upgrade the threat level of certain American Christians here. This recent article from Phil Torres at Salon.com outlines a brand of American Christian extremism that is embraced (or at least pandered to) by several Republican candidates for president, Ted Cruz foremost among them. Not fringe weirdos, but presidential candidates. There is a strong "end times" theology at work among these Christians that sees a violent conflagration in the Middle East as a good thing, since it ushers in the Apocalypse. This is something that ought to be common knowledge in the US, but sadly isn't. Actually Hagee's extreme views came up when John McCain sought his support in 2008, but amnesia set in somewhere along the way, as it always does. Frank Rich wrote about Hagee in 2008 at the New York Times.