Mill and Sidgwick both responded to something like your point 2 by agreeing that motivations don’t correspond to utilitarian math. But they didn’t think that was a fatal problem. They recommended that we start where we actually are, motivationally speaking, and move in the recommended direction. In modern terms they were “indirect utilitarians”, e.g. Mill is sometimes viewed as a rule-utilitarian. Not that I want to defend utilitarianism, but you may be overlooking more steelmanned versions.
I basically agree with your point 1, at least when it comes to normative ethical system-building.
Mill and Sidgwick both responded to something like your point 2 by agreeing that motivations don’t correspond to utilitarian math. But they didn’t think that was a fatal problem. They recommended that we start where we actually are, motivationally speaking, and move in the recommended direction. In modern terms they were “indirect utilitarians”, e.g. Mill is sometimes viewed as a rule-utilitarian. Not that I want to defend utilitarianism, but you may be overlooking more steelmanned versions.
I basically agree with your point 1, at least when it comes to normative ethical system-building.