"The Wire" will always be a show about defeat.
The show's thesis statement is that, in the world in which the series takes place, no one wins, one side merely loses more slowly (this is, in fact, one of the many quotable lines from the show).
"The Wire" portrays the inner city of Baltimore (and, by extension, every major crime and poverty stricken metropolitan area in the United States) as being culturally annexed from the rest of the country. The complexity of the problems which face Baltimore -- everything under the sun -- is so intricate and advanced that, in reality, none of the normal rules and regulations realistically apply. Murders are tolerated, for no other reason than there simply isn't the man power to stop them. Drug dealing is excused. Police chiefs are allowed to "juke" their crime stats. Senators are permitted to accept dirty money to fund their campaigns. The reality of the situation has, in fact, slowly but surely evolved the laws and common practices of an entire city (one that is housed within a first-world, uber-civilized nation) in order to reach something resembling decency.
For example, Omar, the shows ghetto Robin Hood who makes a living killing and robbing drug dealers (though not necessarily in any attempt to bring justice to the world) is allowed to more or less roam free -- the police leave him alone, and even lend him a hand from time to time. His murders and thefts are overlooked, because he's not hurting "taxpayers." This is roughly where the line is drawn. Dealers can kill dealers, but they can't kill citizens outside "the game." Thus, to some extent, the show portrays a degree of moral relativity that the city has created out of necessity. They've rewritten the books without ever picking up a pen. But the key here is that as long as it is possible to pretend that Baltimore is following the same rules as everyone else -- as long as everyone can still choose to see the situation as they wish -- everything is fine. Just don't, for God's sake, acknowledge reality. In fact, when one of the characters -- an earnest police commander, one of the show's few wholly positive figures -- attempts to get the city to formally endorse the legalization of drugs in certain parts of town (in an attempt to reduce violent crimes related to maintain drug dealing turf, which it immediately does), he is promptly fired (after decades of service) and has his pension reduced. He acknowledged reality, and then he forced everyone else to do the same.
My argument here is that the problems have become so advanced, that fixing them is no longer a viable option, and those who try will end up causing more work and complexity by the time he's done. The point is to maintain the lines that have been drawn. The dealers are allowed to operate in certain parts of town, to kill each other, but they have to follow the informal rules that have been established over the years. So, in effect, no one wins, one side just loses more slowly.
Each side of the equation is a part of the same society, and the society at large is slowly crumbling. There are no heroes, no winners. Those that make it to the top -- the police chiefs and mayors and drug lords -- just have all the higher to fall from. And fall they will, probably by the end of the season. No one is immune. Because "The Wire" sees this struggle as doomed from the beginning. Slowly but surely the world is devolving, and each year the infected area swells just a little. It's a plague. And perhaps worst of all, people are getting rich off it. Maintaining the status quo has made careers. Those willing to turn their heads, or even jump right into the deep end, like the show's most dubious character of all Senator Clay Davis, often stay atop the mountain for the longest. So what does the show offer as a solution. This is where "The Wire" shines, as it offers no solution. The show is smart and complex enough to realize that there is no single solution, no single cause of the city's matrix of trauma. In this sense the show is very much like a Gus Van Sant film.
Below is my favorite all-time moment in "The Wire" -- possibly my favorite moment in television history. It's about taking a problem and stripping away all of its context that feels so important, and then just focusing on this: you want it to be one way, but it's the other way. It's that simple. Meditate on that. Accept it. That is life.