Where I live, Wal-Mart sells groceries and other goods that are life-sustaining to lower-income customers.

We've got other stores (Kroger, etc.), some of their goods might even be of better quality. But the price difference is remarkable.

I don't see how de Blasio can really justify denying shutting Wal-Mart out while letting Amazon in.

Seems like a false connection - putting a Walmart in NY creates additional competition for local retail. Putting an Amazon HQ-dot in NY has basically zero retail impact.