I agree with Freemon and McNulty.  Sometimes the ends do justify the means.  For the wire dynamic duo, there was a hitman and hitwoman that dropped upwards of 20+ bodies in the vacants.  They knew who the killers worked for and why they were killing those people, so they took it upon themselves to correct the wrong by any means neccesary.  

The fact that the Mayor was cutting funding for the police force to a point where they could not work 20+ unsolved homicides is what made me agree with it.

Now on the shield you had more of a moral dilema.  Vic and the strike team took money from drug dealers.  In effect they like the Major Colburn (bunny on the Wire) had a handle on who was dealing and set rules which the dealer had to follow.  Me i think i would be more of a Vic than a McNulty.