Buffett has earned economic power by proving he uses it efficiently. He clearly has a good sense of where to put money such that it creates disproportionate value for society at large, where 'good' here means better than millions of others attempting the same. His investments encourage and empower companies to think in longer terms. He has pledged to give it all to charity and has already made good on a record breaking 50B of that pledge. He's not a great foil to use for criticizing capitalism.
>There should exist no single person with the amount of economic power that Buffett has
Why not, then? From a consequentialist utilitarian perspective, we seem to be much better off with Buffett being allowed to do what he wants with his money. From a deontological rights perspective, we reach the same conclusion.
Should anyone be allowed the political power of a US president or senator or mayor?
>contracts are based on laws and capital writes the laws
This seems to lack substance. If I agree to do task X in exchange for reward Y, enforced by the law saying I have to honor what I agree to, and you think I should be getting Y+Z, is your issue really that the law was written by capital? AFAIK, most contract law restricts what I'm allowed to give away and guarantees that I get a minimum in return. Is there a particular law governing contracts that, if removed, would move things in the direction you prefer? Because otherwise I'd think you'd be quite happy with the 'you can't trade your basic rights away, you can't sell yourself into slavery, you must make at least minimum wage, etc.' that we've already got (and that you allege capital is resposible for) and seeking an additional 'you must capture at least 75% of the value you create' or something. Unless you're fundamentally opposed to contracts in general?