It Is Human Nature To:
Have some good traits and some bad traits.
Segregate into in-groups and out-groups.
Judge an entire out-group by the worst traits of its worst members.
Judge one's entire in-group by the best traits of its best members.
Feel righteous in this judgment.
Work to fortify the collective sense of righteousness within the in-group.
Glorify the honorableness of opposing, fighting, converting, or eliminating the out-group.
Never see the mutuality, irony, and destructiveness of this competition.
Privately believe this list applies to everyone except oneself.
Yes to all with the possible exception of the last point, as some of us are acutely aware that we are not immune to such. Tribalism runs deeper in some than others.