A Darwinian defense of Kantian ethics in 233 words

Someone who rejects your friendship when you are being both kind and sincere—that one has core wrongness. Hating someone because they cause something you hate—that is instinct. It is a mechanism of behavior modification that has been selected for. If some cells really do irritate large numbers of others, their anger, expressed as punishment, modifies the irritant’s causal output. An organism’s displeasure, multiplied many times over, effects behavior modification under the power of averages. So the members accidentally serve as powers that determine the social collective as well. Since primate existence originated as already collective (pack-like), it is certain that our tastes are in line with the fitness of the pack. Our tastes are universal and moral because we inherit tastes that exist because, as a whole, they have modulated behavior in a pro-pack-survival way.

So you hate me because I don’t do the dishes, or (you thought) insulted you, or secretly dislike you so you beat me to is—all that is natural since it rests on pro-social pain mechanisms. But if I am kind and genuine and you reject me merely because I am a counter-self, then you have committed the Kantian-level error. Because an existing human that hates humans for existing really is a self-defeating maxim of action. Misanthropy as such is the one bad thing that alone fails Kant’s test.