It's not. That's part of the research. From the article:
> "Indeed, Walmart’s many defenders argue that the company is a boon to poor and middle-class families, who save thousands of dollars every year shopping there. Two new research papers challenge that view. Using creative new methods, they find that the costs Walmart imposes in the form of not only lower earnings but also higher unemployment in the wider community outweigh the savings it provides for shoppers. On net, they conclude, Walmart makes the places it operates in poorer than they would be if it had never shown up at all. Sometimes consumer prices are an incomplete, even misleading, signal of economic well-being."
Walmart privatizes its profits and socializes its costs: https://news.ycombinator.com/item?id=42505420