Wow Jack - you have written this with palpable zest! Electric, succinct, direct writing. Thanks so much, a pleasure to read. I am bookmarking this to read again and again as there's so much to take in!
My theoretical take on this is based on Jonathan Haidt's excellent book - The Righteous Mind. This goes someway in explaining why we are so tribalistic, when it comes to politics. We are essentially intuition-driven information processors, constantly scanning the world around us, morally interpreting information and colouring narratives with our unique worldview. We readily allow intuition to lead us and then use our rationality to come up with evidence to support our beliefs - the absolute arse-backward way it should be. A liberal worldview pegs a conservative as a traditionalist, xenophobic, capitalistic, flag-waving, tax-dodging, climate change denying, warmongering, pseudoscientific, Churchgoing, anti-vaxxer incapable of rational thought. Whilst to the conservative, a liberal is a virtue-signalling, tree-hugging, anarchist vegan gay snowflake citizen of the rainbow-world.
I'd really appreciate if you could read my article and feedback - the parallels between your take for WHY we are so polarized, enraged, partisan, seemingly undemocratic and HOW our brains are literally wired to be this way according to Haidt, are uncanny.