Do you agree that the fairest system would be to combine everyone's utility functions and maximize them? Of course somehow giving everyone equal weight to avoid utility monsters and other issues. I think these issues can be worked out.

Anything you can do maximizes some combination of people's utility functions. So it is trivially true that the fairest system is a system which uses some combination of people's utility functions. Unless you can first describe how you are going to avoid utility monsters and other perils of utilitarianism, you really haven't said anything useful.