This interview has just came to my attention:

Note: I would add here that spree killings are becoming more common in the United States as we move further and further away from the Confederacy. Of the 70 mass shootings since 1982, 33 of them have happened since 2006. If the Confederate flag was driving spree killings (no one seems to have thought so after Columbine or Sandy Hook), they should be becoming less common and should be confined to the Southern states, but that’s clearly not the case.

Instead, spree killings are overwhelmingly driven by things like morbid fantasies, extreme individualism, mental illness, cultural breakdown, social isolation, and an overwhelming narcissistic desire to express one’s own individuality, and a guarantee that “manifestos” will be publicized by the 24/7 cable news media and clickbait websites. Not unlike Caitlyn Jenner or Rachel Dolezal, evil people also yearn to realize their True Selves and are becoming less restrained by traditional moral norms.