I don't fully agree with Aaronson's take, I just think it's underappreciated. I am a sorta-rules utilitarian; in contested questions, I think the moral obligation is to behave in a fashion so that the standards by which we act, if universalized, maximize beneficial outcomes. And I think there is an argument to be made that getting rich people to donate is a thing that a moral system that tries to lead to good outcomes,
should focus attention on.
Like it or not, we have set up our society so that economic decisionmaking power is to a large part concentrated in the hands of a small fraction of the population. This population is a moral fulcrum; the things they decide to do have a significant effect on actual events, in some ways even outstripping governments (which generally hold obligations on par with their power). I think an effective morality needs to acknowledge this and make special dispensation for these people if they decide to bend their power towards creating good outcomes, whether or not one approves of their existence in the abstract.
Assume you are trying to invent a morality to sell to the one percent. The pass-or-fail condition is that this morality must absolve their sins. It seems to me that the default option here is laissez-faire libertarianism, which has cultural bias against doing work to improve the worse off; in my view, being able to make inroads in this moral market is a significant victory for EA and good outcomes in general.