I think you nail something crucial about The Wire in your last couple of comments. This isn't a show about black and white (so to speak); it's about grey. It gets into those areas where absolutes aren't possible, and it explores them with a tenacity that you rarely see in any medium, ever. For example, I don't think we're invited to cheer as the police beat down Bird at the end of the episode; the show makes a point of telling us that he's still cuffed as three or four people jump him, and nothing justifies that. It's not a good side/bad side story. Sometimes the show gets to the point where the drug trade becomes almost a McGuffin, because the show is so deeply invested in the characters as people.