Missie: it's great that your mother has a good job, but the negative perception of WM is drawn from a great many sources, not just personal knowledge. [I worked at Sam's Club long enough to see some of the tactics for myself.]
When publicity forced WM to change some policies, they did, but I don't believe they reformed their corporate culture at all - they just found other ways to maximize their profit.
The Waltons didn't become richer than God by sticking to Sam's vision [I don't believe he'd approve of what his namesake has become], and IMO, the 'bigger is better' business model is terrific for generating profit for shareholders, but not so good for everyone else.
You are correct that big boxes drive smaller businesses out of business, but there's a reason that monopolies are frowned upon, even in a capitalist society. I'm not saying they are monopolies, just that the line is pretty blurry, and in today's pro business climate, what keeps them from crossing it?