Moral compromises

What I absolutely loved about The Dark Knight movie was (beyond that they _finally_ got the Batman and Joker dynamics I love so much from the comics right on the screen) was that there was no black hat/ white hat oversimplification of the heroes or villains. How far do you have to go, how many compromises must be made for the greater good (or bad if you're a mobster).

On a tangent to that, Microsoft was basically started by a few thefts originally, but now the Bill Gates Foundation is doing some amazing, incredibly worthwhile work.
So how many bad things are acceptable for future good things?

Where do you draw the line?