Despite a considerable amount of research, a definitive consensus about Wal-Mart's effect on local communities is hard to declare. And it's not for lack of effort. Arguably, no firm in the history of commerce has been more scrutinized. Business schools routinely analyze successful firms to discover their secrets of success. But Wal-Mart is one of the few businesses routinely, even energetically, put under the microscope to look for its dark side, to determine whether its genes are compatible with a community's DNA.That's not to say there are no conclusions whatsoever from the research. In fact, there are conclusions both damning and supportive of Wal-Mart. This is the likely source of the debate's din: When there is doubt or disagreement, talk louder.