One common factor in the spate of recent multiple mass killings is mental illness. All of the perpetrators were mentally ill.
Availability of guns and knives may contribute. Marriage instability may contribute. Perceived sexual achievement glorified in media may contribute. Peer rejection may contribute.
Mental illness is still perceived as shameful and psychological treatment is often embarrassing. Those afflicted suffer in silence or man up and push on.
Or try to.
When they can no longer endure the pain, we all suffer the results.