That argument would hold more water if the economy were a zero-sum game.
It's fine if the wealthy choose to give away some or all of their wealth, but it must be voluntary. Anything else is called "theft" - or the closely related concept of "taxation".
the article seems to be OK with it being voluntary (more or less?). I think it's just making the point that it's immoral not to give it away. maybe instead of "stealing" excess wealth we can just shame it more than we do now.
From the essay: "For example, it is sometimes claimed that CEOs get paid too much, or that the super-wealthy do not pay enough in taxes. My claim has nothing to do with either of these debates. You can hold my position and simultaneously believe that CEOs should get paid however much a company decides to pay them, and that taxes are a tyrannical form of legalized theft."