Ultimately consequentialism requires you to adopt some set of moral axioms that define what ends are good. If you adopt zero such axioms, then you're back at nihilism. Once you have your minimal set of axioms, you then reason about consequences of the action to try to figure out its likely effects on net utility.
Most consequentialists adopt a "golden rule" sort of axiom about minimising suffering. An alternate formulation is about maximising agents' preferences. Generally people's intuitions about morality are broadly similar, so the challenge is to handle the corner cases most efficiently. But the basic moral relativism problems don't occur for consequentialists.
It's difficult to arrive at a plausible set of moral axioms that are going to lead you to positions such as "homosexuality is unethical", "might is right", or "slavery is ethically neutral". Very few consequentialists arrive at these positions, as far as I'm aware. Some consequentialists do end up back at what are essentially deontoligical positions, however, by re-deriving them consequentially. They argue that it's ineffective to try to reason ethically on a case-by-case basis. I think this is an empirical question about what is practical for most humans.
Most consequentialists adopt a "golden rule" sort of axiom about minimising suffering. An alternate formulation is about maximising agents' preferences. Generally people's intuitions about morality are broadly similar, so the challenge is to handle the corner cases most efficiently. But the basic moral relativism problems don't occur for consequentialists.
It's difficult to arrive at a plausible set of moral axioms that are going to lead you to positions such as "homosexuality is unethical", "might is right", or "slavery is ethically neutral". Very few consequentialists arrive at these positions, as far as I'm aware. Some consequentialists do end up back at what are essentially deontoligical positions, however, by re-deriving them consequentially. They argue that it's ineffective to try to reason ethically on a case-by-case basis. I think this is an empirical question about what is practical for most humans.