I agree. It may mostly be taboo because it's highly individualistic. It's a very big decision to make for yourself, but there are so many systemic influences looming over you.
Put bluntly, every individual is an investment. Parents, guardians, and government funds have gone to birthing and growing a human being. All those meals, clothes, the buildings that shelter us, education, no matter how unhealthy/ill-fitting/asbestos-padded/brainwashing, all of that comes from the effort of other people.
After all that investment, there's an underlying imperative to give something back, even if you're horribly unhappy with being a cog, or everything is a pretense, or you truly live in unbearable physical or emotional pain. Or if you fantasize about death being mainly about leaving a good-looking corpse, and finally being the center of attention and lauded as the paragon of humanity that you always were
, however contrary the reality would be.
The message of, "Don't kill yourself, because suicide is a permanent solution to a temporary problem and life really is beautiful" tends to ring very hollow to me, because I never get the sense that people who say that either know or care what it's really like to want to die. They just want the suicidal person to think the same way and see the world the same way as they do, when theirs is not necessarily a more logical or realistic point of view.