Can you recognize this signature?

Across all ideologies investigated by the researchers, people who endorsed “extreme pro-group action”, including ideologically-motivated violence against others, had a surprisingly consistent psychological profile.

The extremist mind – a mixture of conservative and dogmatic psychological signatures – is cognitively cautious, slower at perceptual processing and has a weaker working memory. This is combined with impulsive personality traits that seek sensation and risky experiences.

The first thing that crossed my mind is somebody who misses the funniest part of a joke, or wildly misinterprets the joke. I must admit I often throw something out when I first meet somebody, in an unconscious(?) attempt to gauge their personality. It's a faulty, self-centered approach, because you have no way of knowing what they're dealing with at the time. But it is surprisingly accurate. Here's more on their findings:

Conservatism and nationalism were related to greater caution in perceptual decision-making tasks and to reduced strategic information processing, while dogmatism was associated with slower evidence accumulation and impulsive tendencies. Religiosity was implicated in heightened agreeableness and risk perception. Extreme pro-group attitudes, including violence endorsement against outgroups, were linked to poorer working memory, slower perceptual strategies, and tendencies towards impulsivity and sensation-seeking—reflecting overlaps with the psychological profiles of conservatism and dogmatism.

Cognitive and personality signatures were also generated for ideologies such as authoritarianism, system justification, social dominance orientation, patriotism and receptivity to evidence or alternative viewpoints; elucidating their underpinnings and highlighting avenues for future research.

There's quite a bit of crossover between violent extremists and garden-variety conspiracy theorists:

More than a quarter of the American population believes there are conspiracies “behind many things in the world,” according to a 2017 analysis of government survey data by University of Oxford and University of Liverpool researchers. The prevalence of conspiracy mongering may not be new, but today the theories are becoming more visible, says Viren Swami, a social psychologist at Anglia Ruskin University in England, who studies the phenomenon. For instance, when more than a dozen bombs were sent to prominent Democrats and Trump critics, as well as CNN, in October 2018, a number of high-profile conservatives quickly suggested that the explosives were really a “false flag,” a fake attack orchestrated by Democrats to mobilize their supporters during the U.S. midterm elections.

One obvious reason for the current raised profile of this kind of thinking is that the last U.S. president was a vocal conspiracy theorist. Donald Trump has suggested, among other things, that the father of Senator Ted Cruz of Texas helped to assassinate President John F. Kennedy and that Democrats funded the same migrant caravan traveling from Honduras to the U.S. that worried the Pittsburgh synagogue shooter.

But there are other factors at play, too. New research suggests that events happening worldwide are nurturing underlying emotions that make people more willing to believe in conspiracies. Experiments have revealed that feelings of anxiety make people think more conspiratorially. Such feelings, along with a sense of disenfranchisement, currently grip many Americans, according to surveys. In such situations, a conspiracy theory can provide comfort by identifying a convenient scapegoat and thereby making the world seem more straightforward and controllable. “People can assume that if these bad guys weren’t there, then everything would be fine,” Lewandowsky says. “Whereas if you don’t believe in a conspiracy theory, then you just have to say terrible things happen randomly.”

That last part is very important, especially when you're trying to figure out why a seemingly intelligent (or not glaringly stupid, anyway) person would allow themselves to believe the unbelievable. There is a certain amount of comfort in it, however false and misleading it is.