But what about people unable to work? What about the elderly, the disabled, or, as more and more gets automated, those no longer able to provide more value than robots? If our moral code is limited to "you are entitled to the value you create", then those people would be left out - and I think that's inconsistent with the rest of my moral code.
I don't have an objectively provable rule, but I do have one that makes a pretty good starting point: if you create something valuable, you should be able to capture most (or even all) of that value.
of course, no one just creates things from scratch. they use tools designed by other people, they use resources extracted from the earth, their productivity might be multiplied if directed by a good team leader, etc. if you take the final product and subtract all the tools, resources, and infrastructure used, you have your personal contribution. I think we should strive for a system where the worker keeps as much of their contribution as possible. some people's contribution will be much larger than others', depending on their skills and the type of work they do, but I don't think this is inherently unfair if you have first accounted for all the external things they have benefited from.