What Makes Someone Support a Bully?
https://www.psychologytoday.com/us/blog/the-couch/201908/what-makes-someone-support-bully
I will admit to the "remaining passive" group many times, but I've also defended the victim and sometimes lost (
but also sometimes won).
I'd like to think that I've never followed a bully or been the bully myself, but you never know what other people think until you ask them, and their answers can be very surprising.
So to answer your question; FEAR
Fear can make someone join a group or do something to prove that they belong to that group.
Fear can also make someone NOT join a group, because they do not wish to have restrictions on their freedom and be forced into compliance and be dominated over.
Some people will only join a group if they can be the leader, again fear of being under someone else's thumb.
Name a person or group of persons and one can explain fear as the motivator if they wish to and work at it. It's not always apparent, but it's there.
Why do some people want harmony (
Conflict Avoidance)? Fear, fear of being singled out and being victimized.
Why do some people want conflict (
Combativeness), just too much testosterone? Fear, fear of being without, and having no rewards.
Maybe we are just wired to fight and cannot evolve above base animal instincts?
Some People Just Like to Fight
https://politicalviolenceataglance.org/2014/02/03/some-people-just-like-to-fight/
If things were as simple as those that seek conflict think they will not lose, and those that avoid conflict think they will not win it would be a much simpler world than it actually is.