The last scene of the movie shows Gordon smiling to himself as he leaves the home of the drug dealer who ordered his partner's death, having planted a bug. One possible is that he shares Gordon's satisfaction that the bug has been planted and that the War on Drugs will continue, but, as I have indicated, this is very hard to believe within the structure of the rest of the movie ,which shows that the War on Drugs cannot be won. Another possibility is that Soderbergh is playing with the audience, allowing us to see through his happy ending to the film's darker implications. Good art sometimes makes you work to understand it. I hope that is true, but still cannot dismiss the possibility of a more cynical explanation.
Audiences expect one buddy to revenge the death of another.
Soderbergh decided to satisfy this audience expectation, even if it undercut the message of his film. If the third explanation is the correct one, we must admit that Soderbergh would not be the first artist to dampen his message to improve his profits. Still it seems a shame. Least of all the director.