Humans are a herd and tournament species, meaning their behavior is inherently violent, group-minded, hierarchical, collectivist, and conformist, and biological determinism plays a big role. Humans feel the best when they have established dominance or punished an enemy they've dehumanized. They need that feeling of "the enemy" to take down and obliterate, and a blind loyalty to their own clan and its leaders. This is why nearly every argument has two black-and-white sides with nearly zero middle-ground; 99% of people do not arrive at such conclusions by their own merit, but through loyalty to their tribe and hatred of "the enemy" one. And if any middle ground ever does exist, it is not recognized; both sides will merely attribute it to the other one. This is not how the real world works, this is how human instincts think it does. The excessive violence and authoritarianism of humans is explained by the ultimate desire to crush and obliterate whoever "the enemy" is, even when doing so is completely pointless. And unfortunately, the desire to identify an enemy to destroy is ever-present, meaning that even if there is no real conflict, humans will find an enemy in something silly or at worst, innocent, out of desperation to quench this instinct.
Within their tribes, humans love collectivism and defined social organization. Everyone follows pre-defined stereotypes and roles so it's easy to make all your judgements about someone by looking at them. Our bodies and brains develop in certain ways to fulfill these social roles. If someone falls out of line, it must be dealt with. If they do not oblige, they are disloyal and must be part of "the enemy". Individualism is tolerated to a degree but only when it's beneficial to the tribe. A good example is how women are afforded much greater freedom with their lives than men because they always have "I can bear children" to fall back on. Whether they intend to or not, or are even able to, humans make quick judgements based on what they see and will assume that she is fulfilling her social duty that way whether it's true or not. Men, however, must prove their loyalty and benefit to the tribe with actions and achievements, or they will immediately stand out as individuals among the brainwashed collective.
Anyone on the outside looking in would be horrified. Even the freest possible human community is very close to communism in absolute terms. Humans on a fundamental level are no different than horses or wolves or other herd animals who are defined by their membership in a collective and aren't allowed to have any life or mind of their own. It's just that these herds manifest in a much larger and more powerful scale in humans.