[B]ecause their instructions to kill supposedly came from their god rather than from random psychic noise, they’re considered “religious extremists.”
That’s too polite. It subtly helps limit their responsibility for their behavior. Of course, that’s a primary goal of religion—to codify the ways in which people are not in charge of this world, and to provide a vocabulary for not thinking about difficult things. That vocabulary is called “faith.” Faith is the exact opposite of thinking. It’s therefore in opposition to others thinking.