We’ll always have a shortage of time to make the calculations before we have to act, we’ll have a shortage of relevant information, we’ll be biased by our own interests and cognitive errors, we’ll have weakness of will, we’ll never know how our actions might influence things in the long-run (especially as precedents), and it just generally will always be too hard to accomplish, so as to be useless.

Maybe that cold, careless, calculating robot could implement the utilitarian software directly, but the human brain certainly can’t; especially not for the thousands of choices that need to be made daily. It would be utterly paralyzing, and almost always go badly. You see, this entire time you’ve been thinking that utilitarians have to calculate utility directly, you’ve been swiping at a straw man Utilitarianism, a misconception about what is going on.

- Peter Hurtford