It's a hard question for sure, because we're only getting a tiny glimpse into the lives of the people we interact with behind a screen. We can't accurately appraise the wishes of another person, especially not via text alone. It can be hard to tell who has reached this conclusion through ample contemplation and deliberation of their particular life circumstances, and who is acting rashly in a moment of weakness, thus making a decision they may regret (which is nothing to be ashamed of btw, it doesn't make their situation any less serious or deserving of empathy)
This space is unique in the sense that you can express suicidality without judgement or recourse, there are no threats of forced interventions or socioeconomic consequences like losing your job, being cut out from your friend circle, etc being hung over your head when you are honest about wanting to die. This unfiltered openness can be a very cathartic thing. However, you're right that it muddies the water a bit when we begin to interact with other users. Do we have an obligation to stop them?
What is our duty of care and how can we quantify it? To 99.9% of society, preventing suicide at all costs would be the goal. Use of force and revocation of bodily autonomy and freedom is seen as a justified and necessary measure. At the cornerstone of medicine and its institutions is the vow to preserve/save life no matter what. To sanction suicide, is to campaign for an idea that goes against the ethos of most cultures, societies, governments, and collective institutions.
Acknowledging that not everyone can be "saved" is completely contradictory to these rules and regulations, even if reality begs to differ. There will always be exceptions to rules, cases that can't be solved, diseases that can't be cured, and in most environments there is 0 consideration for these edge cases. These social codes of conduct are black and white with no room for nuance.
A friend of mine, when I spoke about being suicidal to him, said he had to tell someone. Not out of care for me, or concern, but because in his own words, he didn't want to potentially find himself in legal trouble. That's what the problem boils down too in many cases, and it's just so wrong. Duty of care should come from actual care, love, and desire to help. Most suicide prevention tactics are crafted from a litigious standpoint and designed to reduce risk of liability for any parties involved with the suicidal person.
There is a big difference between genuinely being invested in someone's wellbeing, and simply wanting to avoid a lawsuit. For the people who can be helped, we should do what we can to empathise with them and offer pragmatic suggestions, while respecting their wishes if those solutions don't pan out. I always appreciate when people try to offer ways to help ease my pain or words of compassion, even if I know in my head it's not going to change anything because I've been suicidal for well over a decade.
But for someone else? Those words might just pull them out of the hell they're experiencing. There are often influxes of new users who don't post very often, lurk for a few weeks, then will say they are leaving the site to recover. It's often people who do have support networks in real life, or ways of coping, mitigating and managing their pain, and these individuals actually did go through the classic temporary suicidality that all suicidality tends to get characterised as.
Should those people have been steered towards a last resort immediately? I don't think so. The nature of issues that would make a person suicidal varies so much, and there's a key difference I think between short term and long term problems. I think it's easy to get desensitised to the reality of what we're discussing here, like Pluto said.
After awhile, you do become reconditioned and stop viewing ctb through the lens that most of the world does. It's no longer seems like this very shocking and crisis invoking act, but rather another cruel facet of the universe that you have no control over much like a natural disaster. Thus, you have to harden yourself emotionally to distance yourself from it.
It wouldn't bother me to comfort another suicidal friend because I've seen so much suffering and can handle it, but most people I know wouldn't want to do it or couldn't handle it because they are conditioned to think it's a crisis and they shouldn't have to deal with the risk involved with potentially saying or doing the wrong thing.
So there's both pros and cons to being exposed to such grim subject matter, I think, but I wish I never had to know. There have been several lovely people I met here who passed on. It really hurts to kindle friendships knowing you could lose them at any moment. In the cases of the people that I knew, there was nothing that could be done to help. They'd tried just about everything, and that was the most frustrating aspect of it all. They'd just get accused of not trying hard enough over and over again when in reality they had went through hell trying to recover and never got to experience peace and relief in life. Being told their feelings were wrong only made them worse and worse. Especially when it came down to psychiatric resources not helping them, people just wouldn't believe that these efforts weren't fruitful.
In those cases, I don't think you can do anything but try to empathise and comfort the other person. Just like I don't think people on the fence should be persuaded one way or another, or made to feel they have no options when they haven't tried to improve certain aspects of their situation yet, I don't think we should brute force people into living against their will. I do appreciate that this site takes a harm reduction stance and advocates against methods that won't actually kill you but can cause permanent harm.
I often see smokers outside, sitting on the same benches taking the same drags day after day. These people know that smoking is probably going to kill you eventually, in a very painful way too, yet they do it anyway. We can't yank the cigarettes from their hands, or force them to quit suddenly, even when we know their decisions will eventually have fatal consequences. It's always felt off to me that the world doesn't have this same attitude towards suicidal people who have exhausted all options.
I think we have a duty of care to understand and empathise with others, but I don't think that users of this site can be blamed or held accountable if someone else does ctb. No matter how much you love someone and try to dissuade them, if their heart is set on that decision, they will do it regardless.