I am not sure I am able to provide a satisfying answer, as I cannot even find a concrete angle from which to approach this problem. I would say my path lies in the definition of "right" and how morality interplays on a personal and social level. Does right mean that a person has the ability to interfere in someone else's affairs (with the justification of saving him/her) without fear of punishment or rebuke, either legally or socially; or is it an absolute allowance to act without guilt and with the authority of conscience? I think it often falls in the category of whether one's actions are socially and/or legally permissible, and that seems like a much easier problem to "solve." We have legal systems and cultural norms that often reasonably well define what actions are and are not allowed (whether individuals agree with these societal norms is irrelevant), and these can be applied to the act of saving someone. The real problem then comes with the issue of personal morality.
Even on a personal level, there seems to be a strong influence of societal thought in what gives someone the right to save someone else. This is because it falls in the ambiguity of what should be allowed where the law is not concerned. If someone really wants to drink heavily to the point where it could kill them, is it okay to stop them from doing so? Committing suicide outright is illegal, but living a destructive and unhealthy lifestyle that would lead to an early death is not. Yet it is thought that life is valuable and ideally should be enjoyed happily, so there is a strong current to help/fix those who are unhappy/ill. But all that stems from the belief that life should be continued on. What of those who believe otherwise?
I believe it's very important to try to help other people, mostly because I believe that many people who are unwell do not want to be that way, and would ideally prefer to be happy and healthy. This line of reasoning would then bring me to a point where I would approve of someone trying to "save" someone else to bring them out of misery or to stop them from doing actions that would only lead them to an unhappier state of existence. However, a whole basket full of problems appear at this point. How does one know who is qualified to help someone else? What if someone tries to help but only makes it worse, because they were incapable of helping in a better way or they simply made a mistake? Are good intentions a strong enough justification to take someone's life in your hands (at least to a certain extent)?
I am a person who 'judges' based upon intentions, so I wouldn't necessarily hold someone responsible for a poor outcome. However, I also believe that having good intentions does not make one infallible to criticism, especially if someone trying to save someone else is clearly grasping at straws and doing dangerous things themselves. Having multiple viewpoints is incredibly important, so I would say if one is trying to "save" someone else, they should, almost without exception, not try alone, even if another's involvement is minimal.
A problem I cannot resolve is what you do about the outliers. I believe most people would want a happy, long life. But as with any characteristic or belief, there are those who would naturally have a different viewpoint. I think many, if not all in this category, would be considered in some way mentally ill, because mental illnesses are psychological deviations from the norm. But if someone understood they were going down the path of destruction or to suicide, and they did so purposefully with a clear and rational mindset, I would have a hard time arguing against that. After all, people do sacrifice themselves for others. Would it be correct to save someone who intended to sacrifice him/herself for another?
The lines are all unclear, and at the end of the day all events happen in only one way, regardless of how many possibilities there were and the rights and justifications of those involved. Such is our existence.
