They're easily convinced by simplistic causality arguments that, on the surface, satisfy what they feel is an injustice.
They're not even necessarily wrong about the injustices they feel, but they're too easily convinced about what may be the causes, and how those causes may be solved.
The fact we're talking about militia types indicates a simplicity of thought: enough guns can solve it. So we're starting with a pretty self selected group.
It is some kind of magic that Trump, son of a billionaire, success by nepotism, can have any chance of reaching them.