Shoot first, mostly. For the future, we can eliminate the cultural isolation that promotes such mindsets by encouraging multiculturalism, feminism, queer positivity, other forms of tolerance, and dismantling racist policies and social institutions. Eliminating economic suffering and other social ills that people will seek a scapegoat for will also help. But that doesn't fix the current problem. They consider themselves in a state of social war, if they're so far into this frame of mind as to put it into practice then there's really nothing to do except resist in kind. You can't educate a man coming at you with a rifle.
Sadly I think that encouraging multiculturalism, feminism, queer positivity, other forms of tolerance, and dismantling racist policies and social institutions
will, in the short run, only make increase the violence of these kinds of reactionaries. In the long run I think it's the thing that will make our society a better place.