i agree with you, but at the same time i propose another solution....if i may elaborate on your idea, let us consider the idea of a book:

destiny = author
death = conclusion
reason/existence = theme/essence
birth = introduction

now, by taking this into idea, then despite the conclusion/death the theme/essence still in a sense lives on....if we may avoid any notion of an actual entity of a soul, but instead consider the realm of essence, or idea of essence, then despite the demise of our physical bodies the essence in a sense still exists...now, if this seems like a valid statement, then despite the length of the book, whether it be a 1000 pages or 1 word, the essence will always exist in some form....

therefore, cannot suicide be justified for it merely is the conclusion? however, i am well aware of the argument that the essence is not at its fullest is suicide is the conclusion, but if death is our destiny, and destiny is the author, then our conclusion is at its fullest...

but if you are not satisfied with this idea, then simply take the idea that suicide might limit the full potential of the essence, nonetheless an essence exists....