[Gothbogg the Ripper]

Aragorn, I don't think, would kill Denethor for not stepping down. It would probably escalate into a battle of words and Denethor would most probably end up either exiled or imprisioned, I believe Gandalf warned Pipin that it was dangerous to try and decieve Denethor but Aragorn is more dangerous and the proof of it is that the Army of the Dead answered to him because he was the King of Gondor, plus being a ranger in his past he'd probably met people far more dangerous than a deluded Steward.