[Dominic Harr]

But the claim is not that we should treat altruism and hedonism as wrong, but that they are wrong, objectively wrong - and for that, normative arguments will not do, as then you're committing the fallacy of argument fom the consequences.

A man might prefer to eat cake for breakfast, lunch and dinner (hedonism). But I would point out that, objectively, that man is acting against his own long-term self-interest and happiness.

This is the simplest, most obvious way I can explain what the principle of 'self-interest' means. It is logical, objective, and (I would have thought) obvious.

[general_re]

A man might prefer to eat cake for breakfast, lunch and dinner (hedonism). But I would point out that, objectively, that man is acting against his own long-term self-interest and happiness.

Of course it's "objectively" against what you consider to be his self-interest and happiness, and yours. Now all you have to do is show that your definitions of self-interest and happiness are themselves objective, and not simply your personal, subjective preferences for long life and thinness. After all, this is supposed to be completely objective, right?

It is logical, objective, and (I would have thought) obvious.

It's none of the above, it's simply you defining your values as rational, and other values as irrational. Why is long life better than a short life? For that matter, while you're pondering that one, why not objectively prove that it's better to be alive at all rather than dead?

Have fun ;)