Your Mother, the timeless insult

Why is "I had sex with your mother" such a biting insult to this day? The West isn't a face-based society. Your parents' transgressions don't flow to you. What is it really saying? It's not some medieval shared family dishonor we've carried to the 21st century. If anything, the West is fully behaviorist; neither your parents' failings nor their greatness bestow anything upon you here, so how does the insult persist?

It is an insult of you specifically. Before the sexual awakening, a woman's most important choice in life, which determined the quality of her lineage forevermore, was her selection of mate. She has but a handful of chances in her reproductive years to select the very best genes to combine hers with to instantiate a new human soul that bears her legacy.

If I, a schoolyard bully of yours, was able to convince her to open her legs merely for my moment of joy and for me to later rub it in your face, she is certainly not a discerning woman. She flubbed her life's most important mission. If she didn't choose carefully with me, she likely did not choose carefully with your father, either. This suggests you're a rather low-quality individual, a random person created from whatever muck caught her eye 9 months before your birth. Even if your mother herself was a fine specimen, blending caviar and shit still results in shit.

Having sex with your mother is a powerful insult because even in today's sex-positive, family-lineage-is-irrelevant society, deep down we know that if a woman does not choose her mates very carefully, the resulting product pushed out, you, is essentially trash.