It's an age-old debate whether the end justifies the means. No one personifies it more than Jack Bauer. Technically, he is an outlaw who has violated Constiution of United States than perhaps Osama Bin Laden would ever have. Still, he is a hero. He is the dark knight. Introduction of Agent Renee Walker in season 7 has especially highlighted the choices Jack Bauer makes. It's as if Renee Walker represents Jack Bauer with conscience. Perhaps justifying the quote, "Either you die a hero, or you live long enough to see yourself become the villain". Anyway, in his talk with Renee Walker, season 7 finale, Jack Bauer reveals what he thinks of himself, which in my opinion, summarizes pretty much his behaviour in the whole series. (Mostly harmless. No major spoilers ahead)
"I can't tell you what to do. I've been wrestling with this one my whole life. I-I see 15 people held hostage on a bus, and everything else goes out the window. And I will do whatever it takes to save them, and I mean whatever it takes. I guess maybe I thought, if I save them, I'd save myself."
"Do you regret anything that you did today?"
"No. Then again, I don't work for the FBI."
"I don't understand."
"You took an oath. You made a promise to uphold the law. When you cross that line, it always starts off with a small step. Before you know it, you're running as fast as you can in the wrong direction just to justify what you started in the first place. These laws were written by much smarter men than me. And in the end, I know that these laws have to be more important than the 15 people on the bus. I know that's right. In my mind, I know that's right. I just don't think my heart could ever have lived with it. I guess the only advice I can give you is, try to make choices that you can live with."