What makes it really bad is that you can't add different people's utility functions, or for that matter, multiply the utility function of some imagined galactic citizen by some astronomical amount. The question of "what distribution of wealth maximizes welfare" [1] is unanswerable in that framework and we're left with the Randian maxim that any transaction freely entered into is "fair" because nobody would enter into it if it didn't increase their utility function.

[1] Though you might come to the conclusion that greeder people should have the money because they like it more