I'm not disputing that there are goals/ethics which may be best suited to take humanity along a certain trajectory, towards a previously defined goal (space exploration!). Given a different predefined goal, the optimal path there would often be different. Say, ruthless exploitation may have certain advantages in empire building, under certain circumstances.
The Categorical Imperative in all its variants may be a decent system for humans (not that anyone really uses it).
But is the justification for its global applicability that "if everyone lived by that rule, average happiness would be maximized"? That (or any other such consideration) itself is not a mandatory goal, but a chosen one. Choosing different criteria to maximize (e.g. noone less happy than x) would yield different rules, e.g. different from the Categorical Imperative. If you find yourself to be the worshipped god-king in some ancient Mesopotanian culture, there may be many more effective ways to make yourself happy, other than the Categorical Imperative. How can it still be said to be "correct"/optimal for the king, then?
So I'm not saying there aren't useful ethical system (as judged in relation to some predefined course), but that because those various ultimate goals of various rational agents (happiness, paperclips, replicating yourself all over the universe) and associated optimal ethics vary, there cannot be one system that optimizes for all conceivable goals.
My argument against moral realism and assorted is that if you had an axiomatic system from which it followed that strawberry is the best flavor of ice cream, but other agents which are just as intelligent with just as much optimizing power could use different axiomatic systems leading to different conclusions, how could one such system possibly be taken to be globally correct and compelling-to-adopt across agents with different goals?
Gandhi wouldn't take a pill which may transform him into a murderer. Clippy would not willingly modify itself such that suddenly it had different goals. Once you've taken a rational agent apart and know its goals and, as a component, its ethical subroutines, there is no further "core spark" which really yearns to adopt the Categorical Imperative. Clippy may choose to use it, for a time, if it serves its ultimate goals. But any given ethical code will never be optimal for arbitrary goals, in perpetuity (proof by example). When then would a particular code following from particular axioms be adopted by all rational agents?
But is the justification for its global applicability that "if everyone lived by that rule, average happiness would be maximized"?
Well, not, that's not Kant's justification!
That (or any other such consideration) itself is not a mandatory goal, but a chosen one.
Why would a rational agent choose unhappiness?
If you find yourself to be the worshipped god-king in some ancient Mesopotanian culture, there may be many more effective ways to make yourself happy, other than the Categorical Imperative.
Yes, but that wouldn't count as ethics. You ...
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