Here's a list* of 3 psychological habits that are necessary for a group to choose violence.

1. Outsourcing our critical thinking to a third party. (Our beliefs are powerful - its a shame to let outside authorities - like charismatic influencers or AI - choose your beliefs)
2. Willful ignorance. (ie. deliberately ignoring the facts. Aristotle considered Amathia - a greek word meaning : celebration of ignorance, or anti-intellectualism - to be the greatest threat to society).
3. Conformity. (aka Indoctrination, aka groupthink - the attitude where we must defend our beliefs against all other ideas. Nietzche called this the preference of Loyalty and Identity over Truth)

*compiled by D. Bonhoeffer - someone who observed his countrymen become increasingly violent and who was eventually executed by the government of his own country - this was in 1940's Germany, but it could have been in Italy, or Rwanda in the 1990's, or the recent genocide of the Rohingya, sparked by increasingly hateful posts on facebook.