The simple answer is "no," but few things on this site are simple...
In the broadest sense, the purpose of this site is to help an author (of a story, an RPG, or for whatever reason) develop the "infrastructure" of their story. Stories do and should include topics that make people uncomfortable, whether for the low-brow purpose of entertainment or the noble purpose of questioning the human experience for the purpose of improving the race as a whole.
Having said that, we know that there are limits. The Stack Exchange Overlords have already said that there are arbitrary and undefined limits to how much violence and/or gore they'll tolerate on our site. (We cannot host gruesome depictions of violence, the [torture] tag has it and needs cleaning up). Whether we're facing the reality that people not covered by SE's Terms & Conditions may use the site (e.g., young children) or facing the reality that the subject being discussed is massively personal to an individual, that can't, in and of itself, be enough reason to not ask a question. Were we to allow that, we would quickly discover that no questions can be asked — because just as there is a sucker born every minute, there's also at least one person out there who is guaranteed to be offended by any particular question.
Therefore, there's a difference between what can be asked and how it should be asked
So there is an issue of prudence that we, as a community, expect from users. Querents are expected to ask their questions with a sensible level of professionalism and maturity. This is not the place where people should be getting their proverbial rocks off reading about taboo material. But, as despicable as any one subject may be to any single individual user, it should be the place where someone can ask about any and every aspect of the "infrastructure" of their story.
Before I continue, let me express my belief that this is a two-way street. It is both the querent's responsibility to write a well-asked question, and OUR responsibility (meaning, "everyone not the querent") to help the querent achieve that goal. I'm a fan of closing badly asked questions so quickly that a clap of thunder can be heard — but I am not a fan of excluding (closing, deleting, etc.) questions that can be edited to meet our expectations. If you, the patient reader, are the kind of person to prefer whining or complaining about a question, please consider becoming someone who instructs users in the art of asking better questions. It's so much cooler to "teach the world to sing" than it is to stifle the act of singing.
Hey, you keep using "infrastructure..." wat'cho talkin' 'bout Willis?
This site is NOT an open forum for asking any old question that is refused on every other Stack. We are NOT the dumping ground for any and every question. We do have a purpose and it's reasonably well defined in the Help Center. But, to be brief, it's this:
Worldbuilding.SE exists to help people develop and consistently use the rules and systems for a fictional world of their own creation wherein an infinite number of stories can be told.
Worldbuilding.SE does not exist to help people build their stories, meaning we do not host questions about circumstances, plot, scenarios, or character actions and/or choices.
Having said that, I agree with @MikeSerfas' answer in that the OP of the referenced question was not asking a question about the rules and systems of their world, the "infrastructure" of their story. They were asking a question that was purely circumstantial. Therefore, I agree that the question was closed as "not about Worldbuilding."
But I also agree with @Elimtilas that questions about the rules and systems of a world wherein suicide (or any other "uncomfortable" topic) can occur are intrinsically on-topic.
Nevertheless, I expect such questions to be asked with a sincere overabundance of decorum — because there are plenty enough people in the world who have been deeply hurt by the consequences of suicide, and this site should and must be above causing them more harm just because someone wants to include the topic in a story.
And I believe this to be true and a requirement for any querent asking about any subject that may be deemed objectionable, inappropriate, or uncomfortable. Go ahead and ask your question, but have the good sense to ask it in a way that minimizes offense. If for no other reason than because the Stack Exchange Overlords are watching... always watching...