Jack Shephard - Killer?

In "Man of Science, Man of Faith", Jack tells his future wife that he hurt his ankle running all the stairs in a stadium. When she asks him why he would do that, he answers, "I'm intense." That's as much of an understatement as Ben saying "I lie to people" or Kate saying "I'm a two-timing ho." That second one might not be fair, but you get the idea. Especially after watching "Through the Looking Glass" and "The Beginning of the End," intensity hardly describes Jack Shephard; it's more like insanity.

After Ben tricks him into thinking that Tom just shot Jin, Sayid and Bernard, Jack delivers one of the most savage beatings of the entire series, capped off with a nice "I'm gonna kill ya" to the supposed murderer on the other end of the walkie-talkie. He then tells Kate that once he gets everyone rescued and rubs his success in Ben's face (with a expression that horrifies Kate), he's going to kill him too. After pulling the trigger of a gun pointed at Locke's face, Jack seems to turn into a completely different person - a person ready and willing to kill anyone who gets in his way of getting off the island.

My question is, since when is Jack a killer? This is the same guy who wouldn't torture Henry Gale, and now he's Billy the Kid. After his gun jammed when he tries to shoot Locke (which I'm certain was the island's doing, not the result of an unloaded gun like Locke says), I remember feeling that the Jack Shephard that I knew and loved was gone. To some extent, that might be true. He's a completely different man. His one-track mind at this point in the series (late S3-S4) focuses relentlessly on getting off the island; his old morals and values do not matter.

The one thing that made Jack such an appealing character early in the series was his strong moral compass. He treated decisions of great consequence like the deserved to be treated. Now he's blowing up atomic bombs just to get another crack at a life with Kate. He's still my favorite character, and I admire his unparalleled sense of self-efficacy, but I miss the guy who was more concerned with constantly proving himself and less consumed with guilt and regret.

I have a hard time writing posts about Jack. I've thought a lot about him, but he's such a complex character with such an expansive story that it's hard to capture it all in one post without it turning into War and Peace. I mean, we're dealing with over 100 episodes and about 10 flashbacks/flashforwards. His issues are so inter-related - his inability to let go, his guilt, his desire to prove himself, his insecurities about his father - that discussing one inevitably leads to another, and then you've got yourself about 50 tangents and too many paragraphs. I will work on this. His character deserves it. And if this blog is going to be worth anything to my future self as a documentation of my thoughts and feelings while going through my favorite show of all time, I have to find a way to make it work.