He didn't "as if" the zero-sum argument away.

In the very next paragraph:

> Rather than being drained dry, [the global south] are advancing, growing their share of the global pie even as they deliver better lives to their own poorest citizens.

Unfairness isn't good. They probably agree that things are unfair and should be better.

Hickel is saying ~you're wrong about poverty because the situation is unfair~

Noah Smith is saying ~OK. But I'm not wrong about the fact that poverty is decreasing and the situation is improving.~