Someone can believe in an action being good or bad for a purpose without believing that there is any ultimate reason to choose one purpose over another. Once you’ve assumed very high-level goals, further discussion is about effectiveness rather than morality. Further, except for sub-goals, where goal X is required or useful for reaching goal Y, rationality doesn’t have anything to say about “choosing” goals, which means you cannot rationally argue about morality with someone whose highest goal conflicts with your own.
But ethics doesn’t just apply to these high-level goals. A utilitarian is committed to whatever action generates the most overall net utility—even when choosing how to (for instance) open a pickle jar. (of course, it’s been rightly argued that even a true utilitarian might do best in fact to not consider the question while making the decision, due to the cost of considering the decision). If it turns out (b) results in more overall net utility than (a), then the utilitarian says (a) was the wrong thing to do.
If someone nonetheless thinks one should (a) instead of (b) because one should choose the option that most effectively reaches one’s goals without terrible side-effects, then that person would disagree with the utilitarian above about ethics. If you don’t believe in ethics, then you have no grounds for disagreeing with the utilitarian.
Someone can believe in an action being good or bad for a purpose without believing that there is any ultimate reason to choose one purpose over another. Once you’ve assumed very high-level goals, further discussion is about effectiveness rather than morality. Further, except for sub-goals, where goal X is required or useful for reaching goal Y, rationality doesn’t have anything to say about “choosing” goals, which means you cannot rationally argue about morality with someone whose highest goal conflicts with your own.
But ethics doesn’t just apply to these high-level goals. A utilitarian is committed to whatever action generates the most overall net utility—even when choosing how to (for instance) open a pickle jar. (of course, it’s been rightly argued that even a true utilitarian might do best in fact to not consider the question while making the decision, due to the cost of considering the decision). If it turns out (b) results in more overall net utility than (a), then the utilitarian says (a) was the wrong thing to do.
If someone nonetheless thinks one should (a) instead of (b) because one should choose the option that most effectively reaches one’s goals without terrible side-effects, then that person would disagree with the utilitarian above about ethics. If you don’t believe in ethics, then you have no grounds for disagreeing with the utilitarian.