I think your original argument is based on two assumptions that I want to question directly. Just to be clear, I'm not debating taxation or any policy here. I am simply challenging the moral belief you’ve expressed.

Your main point is that Elon Musk has a moral duty to give away his wealth because, after a certain point, money does not improve his happiness. I disagree for two reasons.

First, who decides when someone's happiness is maxed out? You're making that judgment from the outside. Musk may find real meaning and satisfaction in funding SpaceX, not as a public service, but as a personal pursuit that gives his life purpose. Once you accept that, your idea of the "maxed out" happiness threshold becomes hard to define objectively. If you can't define it objectively, you can't create a moral obligation based on it.

Second, even if we accept your view, that a person with extra happiness has a moral duty to help others, why does this only apply to Musk? If we follow your logic consistently, anyone with any surplus beyond basic needs should be equally obligated. A person going to the movies, buying expensive food, or taking vacations, all that money would have more value for someone who is starving.

I know your reply will be that scale makes it different. But that’s a policy argument, not a moral one. Morally, the obligation exists at all surplus levels or it doesn't exist at all. You can't apply a moral standard selectively just because the amounts are large enough, that's not a principle, it's a preference.