I'm halfsies on the matter. In life, people go through many stages of mental and emotional growth. It's hard to say that their situation or perspective won't change for the better, which is where spontaneous suicide doesn't sit right with me.
Most of the people that I know who have contemplated suicide, or even gone so far as to make threats or attempts, are all alive and well presently. They've surpassed that stage of their life or that mindset and they press on. This isn't to say that the situation/perspective will change for everyone.
For some people, life just isn't cutting it for them. One of my friends has calmly talked about suicide to me for the past 6 years. He has felt the same way at a constant and, although things go well for him in life, he is still indifferent toward it. He isn't depressed or emotionally compromised, but he feels that life can't satiate him (relevant to me, but intj). I can't argue with that and I would find it more selfish to demand he change his opinion. If someone has assessed it, allowed time to pass, and isn't emotionally compromised, it's one of the few times where I can respect their decision on the matter.
So while this friend is still alive and well, if he takes that route at any point, I won't be bitter or angry with him.
I also believe in some degree of selfishness. We're all selfish in this sense. "No, I don't want to live and appease others" "No, live even if it doesn't appease you". Both sides are a different kind of selfishness. You can't condemn someone for selfishness if you are also selfish in your desires for them. It's a touchy, grey area that can have a variety of factors involved.