Humans are tribal.
At our most basic level we want to belong to one group and treat another group as though they don’t have any right to exist (save for giving us someone to hate). Despite this great American experiment and years of both genetic and cultural advancement we remain fiercely tribal. That ardent tribalism comes out most when we talk about politics or religion. Here in America we’ve largely abandoned the religion argument (The Mormons won. It’s been over for a long time) in favor of binary political divisions. This article by Vox voices a clear understanding of how we get to this point so quickly. What it also attempts to explain is why ideology and prejudice are so vitriolic. I believe I already answered that one above: Humans are tribal.
See, it is easier to be ‘right’ when the other side is wrong. It is easier to question their logic than to admit some fault (however minor) in yourself or your thinking as that exposes you to some form of questioning or even ridicule. Take Trump for example. He is having the time of his life, because he grew up in a world where the people with real power always ridiculed him, laughing at his lack of intelligence and silly theories. Few came to his aid when he continued shouting that Obama was a Kenyan Muslim long after the matter had been settled. However, now he is ‘part of the team’ and everyone (on that side of the aisle) is supporting his ideas and ideology. Meanwhile those who once ridiculed are firmly in the outcast set or have come around to his way of thinking. This is what partisanship looks like.
This is also what groupthink and negative culture and cultural decline all look like. We are in a dangerous time. We are normalizing some real nonsense and once that happens it will become easier to normalize even more. We’ve already gone from expecting a certain level of decency from a president to understanding that even the president can and will call people names and there is nothing we can do about it. Partisan thinking is erosive and clearly divisive and is not doing us any favors.