Nietzsche proposed that morality is connected to the individual culture.

I think Gauthier proposed an interesting framework of morality based on Natural Law and Game Theory (Prisoner's Dilemma). This theory shows that mutual agreement/consent and the Tit-for-Tat strategy result in optimal social outcomes, and form the basis of common morality.

I.E. We see in all cultures that theft and murder are considered immoral, and this relates to game theory and natural law. In a small community in the absence of laws, people will tend to form this agreement naturally, as it is benefits the everyone to not have to vigilantly watch for thefts. Even if one person out of a community of 10 were to use his strength to take what he wanted, natural law dictates the other 9 ought to form an agreement to work together as a stronger group to put down the strong individual, and thus even the bully agrees out of self interest, and the optimal condition is achieved by adhering to these agreed upon codes of conduct, and punishing those that fail to practice the optimal strategy and harm the group as well as themselves

In case you are interested in more than my ad hoc explanation that likely does not do these ideas justice, this is the work I refer to. I am a fan of Nietzsche, but admit I am partial to this theory, which is actually quite similar to Kaczynski's writing on morality. No hard feelings if this isn't your bag, I just share because its something I found interesting, and I hold your taste in high esteem

https://en.wikipedia.org/wiki/Social_contract#David_Gauthier's_Morals_By_Agreement_(1986)

David Gauthier's Morals By Agreement (1986) Main article: Contractarian ethics David Gauthier "neo-Hobbesian" theory argues that cooperation between two independent and self-interested parties is indeed possible, especially when it comes to understanding morality and politics.[23] Gauthier notably points out the advantages of cooperation between two parties when it comes to the challenge of the prisoner's dilemma. He proposes that, if two parties were to stick to the original agreed-upon arrangement and morals outlined by the contract, they would both experience an optimal result.[23][24] In his model for the social contract, factors including trust, rationality, and self-interest keep each party honest and dissuade them from breaking the rules.[23][24]