|not really true, but funny|
A less obvious phenomenon is the left-right political dichotomy. The differences are not as obvious because on many issues the right and left have changed sides, such as censorship and the right to free speech. Classical liberalism dominated the 19th century and emphasized negative rights, which only require others to abstain from interfering with you. These are promoted by left and right for different things: the left champions abortion, euthanasia, and recreational drugs, while the right champions economic transactions, guns, and homeschooling. President Woodrow Wilson was widely seen as a Progressive, but as he led the US into the disastrous WW1, leftist intellectuals sought a new term unsullied by this connection and chose 'liberalism,' highlighting the tricky nature of distilling the essence of right and left political views.
One speculative explanation is that the left-right divide is based, if not in our genes, then on our pathogen aversion intuition formed through evolution (see this book, or this online paper). The physical immune system evolved to defend us when pathogens enter the body. Concurrently, humans and other animals have evolved a behavioral immune system, which motivates us to avoid situations where we might become exposed to infection. Feces and rotting flesh are universally considered bad smells, and unsurprisingly contain a lot of dangerous bacteria. Avoiding potential sources of infection has been crucial to our survival, and the motivation to avoid infection remains deeply rooted in us to this day.
Supposedly, this behavioral immune system explains the left-right stance on immigration. If you are hypersensitive to infection the last thing you want to do is to interact with a pathogen source. It operates entirely outside conscious awareness, utilizing the emotion of disgust to motivate avoidance of potentially infected objects and people. Thus it would explain why the right discourages sexual freedom because it leads to sexually transmitted diseases, and also why the right sees immigrants as an infection hazard, the way the American Indians should have looked at the Europeans.
If some people see dangers in immigrants via these deep evolutionary roots, it's difficult to reach a mutual understanding with reason-based, rational arguments. The fear comes from deeply ingrained unconscious systems that one can't control any more than one can choose to like the smell of rotting meat. You can discuss whether immigrants are a financial gain or burden to society, but if germophobes are concerned about an entirely different risk they aren't even fully aware of, such arguments will have no resonance.
As usual, it puts the right into being unreasonable, driven by instinctive heuristics now irrelevant as proven by science in peer-reviewed journals. Such evolutionary arguments are only popular, if even allowed, among academics for understanding bad right-wing beliefs or tendencies. If you apply such reasoning to why women or African Americans act or believe in a certain way, it would be immediately shot down as sexist or racist if you were explaining anything that was not an obviously good thing. Even for advantageous attributes--say why people of West African descent dominate sprinting--it is 'problematic,' because it provides a slippery slope for explaining disadvantageous attributes, perpetuating oppression. Intellectuals are highly attuned to their particular status hierarchy, needing citations, faculty recommendations, and book blurbs. Suggesting the intolerable status quo is not explained by a malevolent cis-white-Christian-hetero pathology marks you a potential quisling at best. Tribalism requires identifying enemies, and also potential traitors insufficiently dismissive of existential threats (or, sticking with biology, a fellow ant infected with the Cordyceps fungus).
I don't find the behavioral immune theory to the left-right divide stupid, just tenuous. My aversion to dirt or sticky things has little valence in my thoughts about immigration, but that's my conscious brain working, perhaps puppeteered by a hyperactive behavioral immune response. In any case, the Covid-19 pandemic is a falsification of this theory. If the right were relatively hypertensive to pathogens, the current left-right stance on easing lockdown restrictions would be the opposite. The right wants to break the lockdown more than the left. One could argue the real factor here is that the right does not value life highly relative to economics, but the lockdown is not just opening up factories, but beaches, parks, and all sorts of places where people congregate.