> So he should drop what he's doing to help the world in the way you want him to?
He can start by not avoiding his taxes. That would be a good help.
> He doesn't owe us anything.
Naive. He owes at least the taxes he avoided. Any business that avoids taxes ends up costing the society more simply because they make use of infrastructure which needs maintenance, it likely pollutes the environment either directly or by proxy, and it ends up exploiting people for their bottom line, people who then need to be financed by the society. He also owes back for the brains he amassed that end up not giving back to the society, brains that were likely educated on the tax payer's pocket.
> He's free to spend his time on what he thinks is important
He is free, but he can also not be pretentious, or put his money where his mouth is.
The argument for helping other people instead of creating new ventures to pat your back is quite simple, but goes over most people's heads; the more scientists we have that actually tackle problems, the easier it becomes to deal with issues like cancer that plague everyone, the rich included. By accepting that the probability that many people smarter than us are impoverished, or born in awful circumstances is large, we see that the expectation that comes from dealing with poverty/lack of education has greater impact on our life expectancy and overall QOL over starting new projects and trying to sample people from a limited pool of candidates.