Anybody notice that when Jack took the gun from Locke, and Locke started telling him, "You aren't going to kill me, Jack...any more than I was going to shoot you at the radio tower..." that Jack actually pulled the trigger?

Only the fact that the gun was not loaded kept Jack from becoming a murderer. Although, if you think about it, he killed the Federal Marshall after Sawyer botched up shooting him in the chest in the first season...and he euthanized Libby by overdosing her with a shot of heroin.

I think he's getting a little close to pyschotic when he gets thwarted, angry, or frustrated.

edit, added: Jack is no longer acting like a doctor. He didn't even check to see if Naomi was still alive. He just left her laying there with a knife in her back. Just like he didn't check or fix Locke's wound after Shannon shoots Locke (the bullet grazing Locke's head) after Boone's death in Season One.

Playing God and All Powerful Leader, rather than Doctor and Healer.

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charlie98210
"Whoa!" she said. "Cry 'Havoc!' And let loose the dogs of war!"
And, like Banquo's ghost, they just won't go away.