Until there's a wealth floor -- until everyone is fed, sheltered and has access to education, there needs to be a wealth cap. We, as a collective humanity, should not allow anyone to have more than, say, $20 million, until the basic needs of others have been met.
The other question is: why $20 million? Looking at the rates on teleport.org, software developers in Nairobi look at the average Silicon Valley software engineer’s pay the same way the latter looks at someone who can earn $1-2 million per year, and I can’t think of any reason why the USA might care to limit its own salaries while other countries catch up.