If you are a terrible person whose actions result in more destruction than benefit to humanity and the planet, then one could argue that you should commit suicide. However, such a person would not do it, because they would want to continue being a bad person. Hence the need to execute people if they are an immediate danger to others. Also it is not proper to encourage anyone to commit suicide, so people would not argue it anyway.
So we've eliminated any reason for why someone
should commit suicide from a collective perspective.
It does have negative consequences for other people, especially those who knew and loved the person; but also for anyone who finds their body. Those consequences should be considered before acting, just as the consequences of any action should be considered before acting. No one can know the future, but it is always possible that if that the person could turn their life around and be happy and healthy, they could do many more actions which would have positive consequences for other people, and that would be cut short if that person were to die.
So there are reasons for why someone would argue against committing suicide, from a collective perspective.
However, all the moral judgments and arguments from others can't ultimately cause a person to act or not; it's always their decision. And most would argue that it would be unethical to try to control another person's actions, as well as ultimately always ineffective. So since people always make their own decisions, even if the decision is to act in accord with another's judgment, it is best to encourage people to make wise decisions.
So we have personal, subjective reasons to commit suicide. Only the individual can know their own subjective reality; other people can provide insight into objective reality.
When a person's subjective reality is consistent with objective reality, we say that person knows truth; when it is inconsistent we say that person is under an illusion.
Since people do not choose death as something enjoyable, because it is our instinct to survive, it follows that all personal reasons for suicide would be under the assumption that all other choices would result in something less enjoyable. This presumes the knowledge of chains of events and where they will lead (concluding that it is to somewhere unpleasant); this cannot be definitively known, since no one can know the future. However, it is possible to predict the immediate consequences of actions, and it is possible to determine which aspects of one's circumstances can be influenced and which ones can't. So to some extent it is possible to objectively determine whether it is reasonable to assume that death is preferable to all other actions. After we have determined which aspects of our circumstances are within our sphere of influence, we can come up with ideas about actions we could take to change our circumstances such that we would have an outcome which is preferable to death.
The best solution for someone who is extremely unhappy includes both treatment of health conditions and healing of emotions, and also the changing of circumstances which are causing them to be unhappy.
If a person concludes that all possible outcomes are worse than death, and that is consistent with objective reality, then they are making a wise and logical decision. This is true in very few instances, such as with terminally ill people, and people who are about to be tortured. Samaurai thought that to live with dishonor was worse than death.
However, most of the time the conclusion is inconsistent with objective reality by objective standards, and they are making an illogical and unwise decision. By objective standards, that person is unable to perceive the existence of other outcomes which would be preferable. In some cases this is true, and the person is simply not thinking clearly because they are overwhelmed by emotion. In others, the person is so unhealthy that any outcome other than death would not be preferable by their own subjective standards because they are unable to enjoy anything. In the first case the goal is to treat the emotion which is overwhelming rational thought while appealing to rationality if the person is so inclined, and in the second the goal is to treat the illness which is causing them to constantly experience negative emotions.
In either case the person is reaching an illogical conclusion, but is unable to effectively use rational thought to solve their problem. So in appealing to the people themselves, it is necessary to appeal to emotion.
In conclusion: suicide is illogical, which is bad by some people's standards; but it is sad that the people are in conditions under which they are incapable of rational thought, or in which death is the most preferable course of action. (And it's sad that they are sad.)
Another greenfairy wall of text.