Greed is at best an incoherent standard. For it to be bad, it has to be pathological.
For the strongest form of the author's argument; that no other system will suffice, ever; it has to be pathological. If I offered you a nice existence with entertaining leisure activities, would your response honestly be to spend the next ten years of your life lobbying for more of the pie? That's a lot of effort to expend - probably without any significant payoff since the return on happiness in terms of extra money drops off - when you could be enjoying yourself instead.
You don't need heaven if people aren't that greedy, (and in my experience - UK based - most people aren't.) Some finite set of resource will suffice.
Charles Koch was interviewed recently, and he apparently believes strongly that creating consumer surplus is more moral than not working.