My two pennies: We had a generation of people raised by baby boomers, people notorious for their inability to manage emotions, or empathize with different or morally ambiguous people. It’s intergenerational trauma from such an upbringing, manifesting as mental illness and marked by delusions of grandeur, paranoia, victim mentality, and stunted emotional and social development. That, and obviously the proliferation of weapons has made mass murder accessible, and in the minds of some people as described above, acceptable.