archimedes11:
As someone who, like you, used to struggle with this issue more than I do now but who has settled a lot as I've gotten older and quieted the part of my brain that would keep me up at night thinking about this -- the same part that fueled many an enthusiastic debate in college and grad school -- I appreciate what you're asking / thinking about.
Let me also out myself as an atheist (well, maybe a 99% atheist) who, mostly as a mostly unthinking & adolescent, has flirted with religion, and who also sees the problem of not being able find a transcental backing to moral beliefs -- to our beliefs, to people from completely different cultures, and all those who hold very different and conflicting beliefs about what is "right" or "just." Indeed, the fact that there can be so much variety in the world of our complicated species in what people claim to know, and that ultimately none of it is provable, and that (except for fundamentalists who I truly believe are in the minority) there will never be a book or any concrete/incarnate example from the divine telling us how things really are, is ... problematic. To say the least.
I'm not really addressing your thought experiment here (though I do find it interesting); I only wanted to offer how I've settled this in my head, as much as that's possible anyway. Essentially it's secular humanism. It's something, I think, you were hinting at in your OP in that we've necessarily constructed societies that more or less allow for a great number of us to flourish, or at the very least survive, and have used as it's basis moral codes that keep us (again, more or less, with varying degrees of success and usually with many contradictions and flaws) from killing one another and to keep us procreating. But for me, like you I'm guessing, morality and ethics are two distinct things that many people conflate; the former is vague and often without reason, and is doled out arbitrarily at times, and overall quite problematic.
I guess I've just let go a lot of my difficulty in trying to justify what is moral and how why we ought to act "morally." It's a piffle. Much like the Cartesian question of how do we know for sure that we exist. Much like many of the debates that try to answers questions that we clearly will never understand. I let, for the most part, folks who want to engage in these arguments have their arguments on their own.
But for me this doesn't mean I can't engage the issues of ethics. I can't justify whatever my personal, highly subjective code of ethics are in a transcendental truth, but that's ok. What I try to do now is live in a way that gives me as much pleasure as I can have while at the same time doing as little harm as possible to others. What I do "know" (as much as it's possible to know anything) is that suffering is real. The pain we can inflict on others is real. I don't want to suffer, and it's safe to say most people don't, so I try not give out something that both I don't want personally, and/or something that would be harmful to the people around me, and by extension to others in the global community as a whole. It's an arbitrary line, and it's sometimes difficult to balance to two. But it's what's allowed me to get through my youth and my 20's & early 30's and to become the very imperfect -- yet mostly at peace -- person that I am today. I try to have compassion for others, even if I can't justify in an objective morality; it's in part selfish because it means I'm at odds with fewer people in the world, and also because it makes for a more civil society. And I'm not interested in living apart from society. And thankfully I'm not stranded on that island you described.
There are two authors/thinkers who impacted me a lot that I figured I'd throw out there. One is someone you might have heard of who's had a lot of critical and popular success recently:
Richard Dawkins. He wrote
The Selfish Gene and the
God Delusion, among others. The second is
Richard Rorty and his book
Contingency, Irony, and Solidarity. It's a bit more academic but somewhat short, albeit dense. Very very broadly, he argues that while we can't prove an objective truth that is contingent in something transcendent, and while we can be ironic about it (that is, we can acknowledge that it's impossible and hold conflicting beliefs that at odds with public "truths"), we can also find solidarity among each and live compassionately (essentially try to be less cruel to one another) without needing to ground that in abstract notions of justice and morality.
Well, that's my two cents. It was nice finding this post and thinking about this for little while today. I probably won't respond again, but I'm glad to have engaged here.
Now back to poker.
Cheers.