Having an us versus them mentality about the world is most consistent with

I believe the answer is: the in-group bias

the in-group bias refers to the attitude of looking  members of our own group more positively compared to non-members, even without any objective reason.
This type of attitude would often lead to a scenario when group members are willing to do whatever it takes for the wellness of their own group, regardless of the damage caused to other groups.

5th to stop bare arms