We know that to wage a nuclear war today, for example, would be a form of suicide; or that to pollute the air or the oceans in order to achieve some short-term benefit would be to destroy the very basis for our survival.
Not only is suicide a sin, it is the sin. It is the ultimate and absolute evil, the refusal to take an interest in existence; the refusal to take the oath of loyalty to life. The man who kills a man, kills a man. The man who kills himself, kills all men. As far as he is concerned he wipes out the world.
It is good to be a cynic - it is better to be a contented cat - and it is best not to exist at all. Universal suicide is the most logical thing in the world - we reject it only because of our primitive cowardice and childish fear of the dark. If we were sensible we would seek death - the same blissful blank which we enjoyed before we existed.