Maximizing one’s own utility is practical rationality. Maximizing the world’s aggregate utility is utilitarianism. The two need not the the same, and in fact can conflict. For example, you may prefer to buy a cone of ice cream, but world utility would be bettered more effectively if you’d donate that money to charity instead. Buying the ice cream would be the rational own-utility-maximizing thing to do, and donating to charity would be the utilitarian thing to do.
However, if utilitarianism is your ethics, the world’s utility is your utility, and the distinction collapses. A utilitarian will never prefer to buy that ice cream.
Maximizing one’s own utility is practical rationality. Maximizing the world’s aggregate utility is utilitarianism. The two need not the the same, and in fact can conflict. For example, you may prefer to buy a cone of ice cream, but world utility would be bettered more effectively if you’d donate that money to charity instead. Buying the ice cream would be the rational own-utility-maximizing thing to do, and donating to charity would be the utilitarian thing to do.
However, if utilitarianism is your ethics, the world’s utility is your utility, and the distinction collapses. A utilitarian will never prefer to buy that ice cream.
It’s the old System I (want ice cream!) vs System 2 (want world peace!) friction again.