Interesting. I don't see Stone that way at all. I think he's trying to get a client off, one that deep down even he doesn't know if is guilty or innocent. He certainly didn't know whether Naz was guilty when he inserted himself in the case.
I do think he's committed to the law and legal principles, so in that sense I agree. He's not crooked, and I think he does believe people deserve a vigorous defense.
But I think his interest in the case and doing a good job is more personal and financial than trying to do good by Naz. I think Stone is an extreme realist, with a bit of a persecution complex, a loser who's getting a bit of a second chance here with a high profile case.
That MAY be no different than what you meant really, I just took your post to sound like Stone is driven by good intentions and Naz' welfare. I think he's way more cynical than that.
I am not saying that's a bad thing about Stone. I think it makes him a much more interesting character than just being a crusading true believer. I think he's an analogue to everyone else...the prosecutor, cops, Chandra, medical examiner...just trying to do their job the way they think they're supposed to. The interesting thing is that all those people are at the top of their profession, and he's basically a cockroach in his. So he's thrust into the big leagues, and more than holding his own. It's an awesome underdog story, and Turturro is playing it great.
Box is a possible exception to everyone basically trying to do their job the best they can, but even then, it seems obvious that he's been really good at his job. It seems implied to me that some combination of world-weariness, melancholy about retirement, etc prompted him to give into hubris and cut corners.