I found a link to an article entitled The Great Walmart Wars via a link on Robert Scoble. The main thesis of the article is that although consumers like Walmart it is actually bad for the overall economy of a region, they don't their employees that highly and they drive smaller competitors out of business leading to homogenization.
I wasn't really interested in the veracity of the claims or otherwise. Instead what I found interesting was the overlap the article had with similar screeds I'd seen against large booksellers like Barnes & Nobles and Borders as well as a number of the rants on "Why Microsoft is Evil" style websites such as What's So Bad About Microsoft? on the No Pity For Microsoft website. The complaint about driving smaller competitors out of business seemed to be an underlying theme in such diatribes.
It seems that at a higher level the problem people seem to have is with the inherrent competitiveness of the capitalistic system. Few would argue that consumers have chosen with their feet that they prefer the goods and services of Walmart, Barnes & Nobles and Microsoft to those of their competitors due to being happier with their prices and convenience compared to alternatives. However the inherrent nature of competition is that there will be winners and that there will be losers. In a way, competition amongst producers in capitalist systems is a Zero Sum Game.
I am curious about examples of companies that have grown dominant in their particular markets without there being parties that complain about similar damage to the ecosystems of those particular markets. This would prove enlightening.