Yeah I think we agree that utilitarianism is held to an unreasonable standard. I think contributing to that is some advocates suggesting it’s a solid utopian model to guide all decisions without further refinement and nuance (and I don’t think this is what you’re arguing).

And because it hasn’t been in practice widely adopted in history (unlike e.g. liberalism or Catholicism) the rubber hasn’t hit the road to allow us to understand how it would work practically. I think some other good ideas suffer the same problem/preemptive attack. Indeed any social progress seems to be attacked by a sort of whataboutism or false slippery slope attack.

To your question on basic principles, I think they’re caught in exercises like the trolley problem or the psychological experiments of the 60s: people on the whole don’t want to be responsible for causing harm, they don’t want to see people in their influence of control harmed, they don’t want to feel bad about themselves, they don’t want to be judged/punished by others - even if convinced it’s for the greater good. I’m not saying some people won’t take a fiercely rational or ideological lens, but on the whole people are influenced by some common psychology. And I think actually this is probably good: as much as it hinders “utopian” ideas being realised I think it ensures humanity moderates ideology.

I think without this a strict utilitarianism, eg a robotic approach, would lead to kinds of harm that I wouldn’t support, even if justified to some sort of ends that itself is subjective. But I think with it, an elevation of the greater good would probably be better than many approaches today. For a practical example I think we should permit more people to consensually enrol in promising but risky cancer research and treatments.

To reiterate that same point I think that in practice those factors would probably allow most systems to be successful, and some/many might be better than what we have now.