Hey, wanderer. I don't necessarily disagree with you, and I appreciate your POV, and the erudite way in which you have expressed yourself. Back to my original question, though, how are we supposed to look at suicidal behavior? Assuming the position of an outside, impartial observer (e. g. An extra-terrestrial), doesn't suicide look like a symptom of mental illness? I mean, how could killing oneself contribute to the propagation of one's genes (assuming this is the ultimate motivating force of life)?
To address your first question of how suicidal behavior should be perceived, I think this depends on the kind of mind doing the perception. Right now, that we know of, we're only aware of our own species' evaluation of suicide. But we are a particular animal with a particular genetic evolutionary, and therefore neurological and social, heritage. Part of that heritage seems to include a strong survival behavioral imperative that, possibly through gene pool selective pressures, has become generalized as a broad (across-cultures) moral precept--that being alive is better than being dead. Although there may be a biological grounds for this belief, it still remains only a belief. So I can't find any obligatory truth to a claim about the value of life or that being alive must be better than being dead. Which means I don't think there is any philosophical reason anyone has to conclude life is either good or bad and therefore that suicide is either good or bad.
I also think cultures should ask whether moral precepts are scientifically objective. If they aren't (like that being alive is a generally better state than being dead), and there is no strong, near-universal philosophical reason the precept should be generalizable (like proscriptions against pleasure-killing of other people), then the mere popularity of a belief (like "suicide is bad") ought not to be legitimized as a formal legal prohibition against others' freedoms to determine their own life course--including when and how to die.
You asked, "doesn't suicide look like a symptom of mental illness?" I find this question problematic. First, it assumes the truth of the phrase "mental illness" as perpetuated by the psychiatric and related professions. As argued, rigorous biological cause-effect evidence has not been forthcoming and both British and European authoritative psychological boards have, in acknowledgement of this, pushed for replacing words like "illness" (which implies a physiological cause) with words like "condition" (which implies a complex interaction of factors, including individual genetic constitution and particular social characteristics). So an intelligent non-human observer might, as you might if you saw heavy calluses on the hands of manual laborers, conclude that suicide is a particular choice related intimately to individuals' life experiences--not initially (as in initial cause) their pathophysiology. Such intelligent observers also might not be biased in their assessment of life-value and so might be no less disinclined to choosing suicide than many Westerners are to reproductive autonomy and abortion.
A quick comment on genetic reproduction. As I see it, this is, like solar radiation, merely a process particularly evolved minds ascribe value to. We recognize that the process of solar radiation is useful to us (agriculture, warming flesh and homes...) so we generally think it's good. Until it's not (increasing temperatures, heat stroke...) The same of reproduction (the children that bring emotional pleasure vs the negative effects of extreme population density...). There is no necessary association between a natural phenomenon (like genetic evolution or the perpetuation of one's own genes in a gene pool--which, mathematically, quickly becomes statistically insignificant due to Mendelian recombination) and a moral evaluation of the phenomenon, frequencies of opinions notwithstanding.
Sorry for a long answer, but I cannot find a single rigorous justification, either scientific or philosophical, for forcing other demonstrably generally competent adults from both drawing (and expressing) conclusions about their own life value and on acting on their conclusions in ways that don't directly and imminently harm others. As I and others have already expressed, no scientist or medical specialist has ever produced corroborable biomedical evidence that "mental illness" is generally caused by neuropathology. If this claim is false, others who hold the contrary perspective should be able to produce the supporting citations to the peer reviewed biomedical literature. In the many years I've been asking physicians, scientists, clinical psychologists, and other professional or university colleagues to provide this literature, no one ever has. Like most other scientists, I'm happy to revise--even recant--my perspective when the weight of high quality cause-effect evidence strongly supports the alternative hypothesis.