I'd have to go back and watch Breaking Bad, but did Mike ever kill a so called "innocent"? The only time I even remember him killing was when he had to save the asian guy who was being held in a warehouse (I forget what that guy's role was). I always think of him more as the cleaner when he was first introduced as opposed to a killer. It's been a while though, so I don't remember many specifics.
The first thing that comes to mind with the whole good samaritan thing though was the kid at the train robbery. He comes across as the kind of guy who will do whatever he has to, but still has that honor code of not involving "civilians" (or whatever you want to call them). That much is retained up until the end.