The purpose of (Objective) morality is for man to pursue actions that forward his life. The purpose of (Objective) laws is to prevent man A from interfering with man B pursuit of actions that forward B's life. Suicide is not an action that forwards a man's life. Why then, should there be Objective laws to prevent A from preventing B from committing suicide? Sure, it's true that A may end up having to use force (e.g., restraints) to prevent B from killing himself. However, since B isn't pursuing a moral course of action anyway, why should the law protect him?
This isn't about the law forcing B to pursue a moral course of action. This is about the law NOT preventing A from pursuing a course of action that benefits A's life by preventing B from pursuing an immoral course of action.
To tie this to Rand's writing, consider the reason that Galt gave for his willingness to die rather than let Dagny be tortured/killed. He stated that without her, all his other values would be meaningless. Does this also means that if she got hit by a bus, die of cancer, etc.; would he consider suicide?
I suppose that this line of reasoning may also allow A to prevent B from pursuing prostitution since prostitution is immoral although not necessarily illegal under Objective law.
Again, my question isn't about whether the government should attempt to prevent suicide. Base on this statement:
"The purpose of government, according to Objectivism, is not to protect a person from himself, but to protect life-seekers from attackers."
I question why should the government protect death-seekers from attackers?
I suppose that I am not clear on whether the following is a moral absolute or there are context around it that should not be dropped:
"Objectivism holds that the initiation of physical force against others is completely evil -- period -- regardless of whether the victim is acting to strengthen his life or to undermine it."
If it's an absolute then so be it. If there are context around it then I wanted to explore what they are; hence the cause for the question.
The question does not accurately express the Objectivist view. The question states:
The purpose of (Objective) morality is for man to pursue actions that forward his life.
This is fairly close to what Objectivism says, though with somewhat less precise terminology than one finds in the Objectivist literature. The purpose of morality, according to Objectivism, is to provide man with the guidance he needs to further his life across the whole of his lifespan, assuming that he seeks to remain alive, and to enable him to do so by methods and policies that apply equally to everyone. (In case anyone tries to interpret every word of this formulation and similar formulations by itself, as a standalone unit not contextually interconnected to the rest of the formulation and to reality, I must add that "everyone" here refers to normal adults.)
Objectivism also does not say (and cannot say) that everyone ought to seek to remain alive. That is a choice that is very easy for anyone to make, not requiring any particular moral guidance, and is presupposed (in the affirmative) by Objectivist morality. Objectivist morality is most concerned not with whether a person should want to live, but with what needs to happen next, for anyone who does want to live.
The next sentence in the question makes a huge leap from ethics to politics without considering the full context by which Objectiviswm justifies the actual transition that Objectivism makes:
The purpose of (Objective) laws is to prevent man A from interfering with man B pursuit of actions that forward B's life.
This is not what Objectivism says. Objectivism holds that the initiation of physical force against others is completely evil -- period -- regardless of whether the victim is acting to strengthen his life or to undermine it. The ban on physical force, according to Objectivism, does not depend on consideration of the purpose of an individual's actions, so long as the individual is not initiating physical force against others.
If the questioner is seeking to argue in favor of a non-Objectivist position on this website, I maintain that the discussion will need to begin with a proper understanding of what Objectivism actually says and why. But so far, the questioner has not said that he seeks to advance an openly non-Objectivist viewpoint.
In practice, the viewpoint expressed in the question would have the effect of severely undermining all individual rights (as the updated question has already noticed in regard to prostitution), since all an infringer would need to do is allege that the victim of physical force by others isn't acting for his own best (long-term self-serving) interests. Every instance of initiating physical force against others would then need to be handed over to a thorough process of adjudication to determine wither the proposed initiation of physical force is "justified" or "unjustified" according to the intent of the victim, before retaliatory force could be approved. The threat would be enormous to those who have their own, possibly revolutionary ideas of what is the best course of action to take in their own lives.
Consider a further aspect of Objectivism's transition from ethics to politics. The purpose of government, according to Objectivism, is not to protect a person from himself, but to protect life-seekers from attackers. How does a person's own actions, perhaps deliberately meant to harm himself, pose a threat of any kind to the lives of others? Who is being protected by such forcible intervention against a self-destructive person, as long as the target of the forcible intervention isn't resorting to physical force against anyone else? This is yet another reason why I see the claim in the question's second sentence as utterly unjustified by any rational, objective analysis, in addition to expressing (thereby) a serious departure from Objectivism's philosophical position.
Additional note: if one looks only at the headline form of the question, "Should it be illegal to prevent a suicide?" -- the first issue that needs clarification is whether or not the context is today's system where laws already exist prohibiting suicide. If all that is being proposed is to pass an additional law that prohibits stopping a suicide, then we will have created a system of blatantly contradictory laws. That is exactly what the anti-trust laws are, and why Objectivism classifies the anti-trust laws as non-objective.
On the other hand, if we are talking about an ideal legal system where there are no laws prohibiting suicide, then the principle of individual rights (as developed in Objectivist philosophy) would clearly extend to the protection of the right to end one's own life. No further laws should be needed, since the laws already implementing the protection of individual rights in general would almost certainly be adequate to protect the right to commit suicide as well. (I must also add here that few today are pressing for the "right to suicide." So many other rights issues are far more pressing today, including the right to engage in production and trade, a woman's right to abortion, many aspects of the right of free speech, and so on.)
Update: The Right to One's Own Life
An update to the question asks: "why should the government protect death-seekers from attackers?" -- and seeks a clearer understanding of why the ban on initiation of physical force applies to a case where the victim of the force wants to die anyway. The latter issue presupposes that the death-chooser doesn't want to be stopped from killing himself. Any forcible attempt by anyone to stop him would then be without his consent and thus an initiation of physical force against him. Hence, the issue is whether or not the law should take congnizance of his desire to die anyway (by his own means) in deciding to intervene against others who might initiate the use of physical force against him.
I maintain that the law should not try to do that, i.e., should not try to mitigate the ban on initiation physical force on the basis of a victim's alleged wish to die. As I explained in my original answer above, there is a serious practical issue with attempting to do that, namely, how can the law positively know that a victim of physical force is an intentional suicide-seeker in all cases? Injecting that kind of consideration into the ban on initiation of physical force would very likely undermine the whole ban severely in practice. If the ban is not conditioned upon the victim's intentions (other than whether or not he is consenting to whatever is being done to him), it is far easier to enforce the ban than if the law needs to pause while a formal judicial determination is made as to the victim's state of mind (beyond the issue of consent). The principle of "innocent until proven guilty" also has a corollary presupposition that unwilling victims of physical force want to live (or very probably do). I.e., life-seeking is the overwhelmingly normal case; deliberate death-choosing is a relative rarity (and far shorter lived).
There is another key point: the existence and nature of a proper government is identified on the basis of the need of life-seekers to be protected from initiation of physical force. The "life-seeking" perspective is presupposed by the whole structure of individual rights and a proper government to protect them (as well as by the underlying code of morality). The possibility of choosing to die is outside of this primary context, but is easily accommodated in the structure of principles after the main structure is identified. The accommodation is for life-seekers to accord the same protection to death-choosers that life-seekers accord to other life-seekers. It is a minimal extension of the main structure and an entirely appropriate and natural extension, causing no harm to anyone and no disruption of the main structure of life-protecting principles. Life-seekers lose no values by being stopped from attacking death-choosers, since life-seekers have no values to gain from death-choosers.
This leads to a more basic issue, as well. The right to end one's life is an aspect of one's right to one's own life. The right to life includes the right to dispose of one's life as one chooses, so long as one does not initiate physical force against others.
I grant that this aspect of the right to life is highly contrary to a "social premise" approach -- the idea that "society" is the fundamental unit of value, not the individual, and that individuals are "society's assets," to be vigorously defended and protected by the "society." Someone on this premise might nevertheless claim that individual rights are the best practical way for a society to protect its "assets" whenever the individuals are life-seeking, but that "society" should try to intervene when an individual wants to kill himself, in order for the society to "protect its assets." So far, the present questioner seems to be proceeding on a different premise, but I mention it in case other readers of this discussion implicitly or explicitly approach the topic of suicide (by normal adults) from the "social assets" perspective.
I must also add that I see nothing wrong with a non-forcible attempt to deter a suicide by someone who cares about someone else who is suicidal, and who wants to help, especially if the threatened suicide is actually a psychological plea for others to help him live. (There are also potential issues of trespass and the like that could justify forcible intervention to stop a suicide, i.e., cases involving violation of the rights of others. The intervention would say, in effect: "If you want to die, don't do it here; this place isn't your property.")
(It occurs to me, in addition, that this issue of protecting a death-chooser from physical force by others is very similar to what I call "the death-chooser dilemma" in a morality that is based on life-seeking. I have previously discussed that topic elsewhere on this website in addition to mentioning it briefly in my original answer above.)