Bret, that's not how being a defense lawyer works exactly, you don't have to believe the person is innocent, nor do you have to even argue that they're innocent.
A lot more goes into it than that, there is a world of difference between "not guilty" and "innocent," as well as oftentimes just fighting to prove the evidence is baseless and the like is the goal of the defense attorney.
Trust me, if you saw the vast inequalities between the prosecution and the defense, especially on the local and state level you wouldn't be so quick to accuse.
Do you know why the War on Drugs has so successfully damaged the urban Black community? Because more often than not, defense attorneys are absent, and/or the ones that are there aren't doing their job correctly. In this case, it was the prosecutor that dropped the ball.