At first Ayn Rand may seem to give a good reason for saying that the initiation of violence is immoral: it forces people to against their own reason:
"To interpose the threat of physical destruction between a man and his perception of reality, is to negate and paralyze his means of survival; to force him to act against his own judgment, is like forcing him to act against his own sight. Whoever, to whatever purpose or extent, initiates the use of force, is a killer acting on the premise of death in a manner wider than murder: the premise of destroying man’s capacity to live.
…
To force a man to drop his own mind and to accept your will as a substitute, with a gun in place of a syllogism, with terror in place of proof, and death as the final argument—is to attempt to exist in defiance of reality. Reality demands of man that he act for his own rational interest; your gun demands of him that he act against it. Reality threatens man with death if he does not act on his rational judgment; you threaten him with death if he does."
However, this reasoning does not make sense, especially considering what Rand says about the nature of reason:
“Man has no automatic code of survival. His particular distinction from all other living species is the necessity to act in the face of alternatives by means of volitional choice. He has no automatic knowledge of what is good for him or evil, what values his life depends on, what course of action it requires. … Man must obtain his knowledge and choose his actions by a process of thinking, which nature will not force him to perform.”
Just because your life is threatened does not mean you don’t stop thinking or that you don’t stop acting in your self interest. If your life is threatened by starvation, you must use your rational mind to find out how to survive. Indeed, Rand herself points out that reason is the faculty by which man chooses a course of action that ensure’s his survival, and that, unlike plants which act automatically, men must choose to act and can’t act automatically.
So, if a highwayman were to point a gun at me and say “Your money or your life!”, I would have to use my ability to reason to choose between possible courses of action: I could give the robber my money, true, but I could also attempt to run away, or to take the gun away from the robber, or to fight and incapacitate the robber. The fact that a robber points a gun at me does not make me act automatically, like a plant: I still must choose to take a course of action that is in my own self interest.
Thus, a threat of survival from the initiation of force is any different from the threat of survival from something natural like hunger: In both cases, man must use his reason to choose to act in his own self interest, to ensure his own survival. This being the case, Ayn Rand contradicts herself: threats of violence do not prevent man from acting in his own self interest, so she does not prove that violence is immoral.
Taking all that into consideration, why should the initiation of violence be considered immoral in objectivist ethics?