No, it boils down to: What kind of world would it be if this was the operating principle? Would "might makes right" set up a virtuous circle of increasing prosperity, or would it create a vicious circle where civilization never would have gotten off the ground in the first place? And which kind of resulting world would you rather live in?No it's not. The claim, after all, is that we must not "act Darwinian," because it's morally wrong. Well, why is it wrong, when it so clearly works well for other species? What is it about our (evolved) brains that automatically excludes us from Might Makes Right?
On what basis can you justify the fact that "decid[ing] for ourselves how to live" must exclude my taking advantage of those weaker than I am?
The answer boils down to this: because you said so.
See, that's where the "enlightened self-interest" calculation comes in: at the end of this proposed principle playing itself out in the long run. That's where the critique of self-interest-based morality always fails. Y'all keep confusing short term, ad-hoc self interest with enlightened self interest. When you're dealing with questions of principle, you're necessarily forced to examine the results of the being used by everybody in similar situations over time - i.e. being used as a principle. And on this level, might-makes-right fails badly, IMO.
Part of the problem is debating these as isolated issues. We are all chock full of conflicting interests. What I do today because the mood suits me may compromise what I'd like to do tomorrow. By sacrificing now, I can enjoy something I value more later. I've heard economics described as more now or much more later.
For some reason there seem to those believe none of us have figured this out. If drugs were legalized, we'd all be zombies tomorrow. If there were no speed limits, we'd all drive around with the accelerator floored. If God didn't tell us not to murder, everyday would be a blood bath. Their assumptions are incredibly wrong. People are just not like that.
Let's see -- China, Mesopotamia, Egypt, Rome, Persia, Mayans, Aztecs, Incas -- all of which thrived by conquest, enslavement, and various forms of brutality, and all civilizations that somehow managed quite well to get off the ground.
And which kind of resulting world would you rather live in?
If a morality boils down to what world I would rather live in, then it is not objective. After all, you probably want your world to be different from how I want mine. In an objective world we takes what we gets, and live with it.
Don't forget: what I'm attacking here is the objectivst claims to have derived an absolute and objective morality.