A Proof of Utilitarianism
From 4 basic axioms.
Utilitarianism can be derived from the following principles
One should do what perfectly moral third parties would prefer they do.
For any possible events, perfectly moral people should prefer the better one occur rather than the worse one.
If something is better for some and worse for none, it is better overall.
Distribution of utility across people is irrelevant as long as the utility is fixed (so, for example, it’s just as good for three people to have 3 utility as for one person to have 9).
The proof will be left as an exercise for the reader.
what do you mean by perfectly moral in 1. & 2.?
You are "hiding" an important assumption that is not necessarily true:
0. There exists a perfectly moral third party.