Most of us abhor the smell of death. Perhaps there is a biological reason for it - being around death may result in one's own death.
Many of us are fearful of those not like us as this is perhaps singularly captured in the following excerpt from the Social Workers Code of Ethics "(d) Social workers should act to prevent and eliminate domination of, exploitation of, and discrimination against any person, group, or class on the basis of race, ethnicity, national origin, color, sex, sexual orientation, gender identity or expression, age, marital status, political belief, religion, immigration status, or mental or physical disability." See: https://www.socialworkers.org/pubs/code/code.asp
One may ask, does the above assertion work, if the political belief in question does not support the above notions? What if the political belief in question chooses to differ on issues such as gender identity or even sexual orientation? Perhaps one resolution to this seeming problem is that groups of differing political ideology be allowed to exist in the same system, apart from the influences of force by other political beliefs. The above list of traits is fundamentally based on being inclusive; however, it has perhaps reached some breaking point, in that, those who differ on the basis of the attributes described, may find themselves "dominated" by that very political belief of inclusion, when separation is what is desired.
What follows will walk through some touchy subjects for more or less all of us. It starts by asking the question: Is rejection of people with attributes such as being homosexual, abnormal gender desires relative to their body's gender expression, just as much a function of evolutionary biology in the same way that an ugly person may not gain as much acceptance as someone who is considered to be beautiful in their external appearance. We are informed that individuals considered beautiful basically have average faces - they are perhaps a 'subconscious' symbolism of the collective of humanity.
Consider the reversion the some have described upon seeing what is called public displays of affection, consider the revulsion some describe when seeing people with obese bodies displaying much of their bodies in public. Likewise consider the reversion and seeing someone who is starving themselves such as an anorexic body which is nothing but skin and bones.
Perhaps the body has mechanisms, hard wired, to find certain things revolting and if you're still not convinced, I return to the smell of death, which is captured in a particular molecule, or the smell of sulfur seen in rotting eggs or gaseous admissions from people and animals' posterior.
Consider that in the the selection of your mate, perhaps there was some level of their appearance that was considered as a factor. If your mate had an extra 200 pounds on their body would you have accepted them? 900lbs?
Whether this revulsion function is biological or mental it's hard to say and it may differ from person to person, as will be explained.
As with taxes, each of us have to draw a line somewhere, surely, a tax rate of 100% is not acceptable, nor is one of 99%, likewise the body mechanism itself, if it is true that I have certain evolutionary components built into it, would naturally cause certain feelings of revulsion to register into the conscious mind, in order to prevent further propagation of such attributes into the gene pool? This form of evolutionary biology assumes that we are nothing more than advanced animals. Perhaps we have an animal side and another side that can also be evolved, a mental side.
Evolution of this mental side may include rising above our basal evolutionary code -- and may include not only revising that code, but learning that others may not have yet evolved their own code to the point of being able to evolve their own code or at the same rate. This may lead us to
And my own journey I'm slowly but Shirley learning as I encounter different mindsets that each one tends to contain a certain nugget of truth although like Princess P it may be wrapped in layers upon layers of other things. The golden is to dig for the nugget of gold, to find the element of truth buried in those perspectives that one may encounter in life. Mother nature or God or whatever term you prefer has Shirley formed such individuals in the same way they have formed yourself.