Interesting. I'm not certain, but I think this isn't quite right. In theory, the westerners would just be sending their money to desperately poor people, so aggregate demand wouldn't necessarily decline, it would move around. Consumption really doesn't create wealth. Of course rational utilitarian westerners would recognize the transfer costs and also wouldn't completely neglect their own happiness. [...] Unless you believe in objective morality, then a policy of utilitarianism, pure selfishness, or pure altruism all may be instrumentally rational, depending on your terminal values. If you have no regard for yourself then pursue pure altruism. Leave yourself just enough that you can keep producing more wealth for others. Study Mother Teresa. If you have no regard for others, then a policy of selfishness is for you. Carefully plan to maximize your total future well-being. Leave just enough for others that you aren't outed as a sociopath. Study Anton LaVey. If you have equal regard for the happiness of yourself and others, pursue utilitarianism. Study Rawls or John Stuart Mill. Most people aren't really any of the above. I, like most people, am somewhere between LaVey and Mill. Of course defending utilitarianism sounds better than justifying egoism, so we get more of that.

I don't think objectivity is an important feature of ethics. I'm not sure there's such a thing as a rationalist ethics. Being rational is about optimally achieving your goals. Choosing those goals is not something that rationality can help much with - the best it can do is try to identify where goals are not internally consistent. I gave a rough exposition of what I see as a possible rationalist ethics in this comment but it's incomplete. If I ever develop a better explanation I might make a top level post.