I am intrigued by this idea, actually. Let's forget about the moral question for a minute. I'm curious how a society would evolve if it started from these unusual circumstances. Suppose 20 people, 10 men and 10 women, landed on this deserted island say 200 years ago. They were regular God-fearing American farmers, we will say. They were common folk -- not too bright or educated, but they managed to survive using basic ingenuity.

Now, 200 years later, what kind of a society would they be? It's interesting to think about this "de-evolution" so to speak. After a couple generations I think they would mostly forget about civilized society because necessity would demand it; but I bet they would have some kind of legend/lore associated with it. A notion of the Christian God would probably remain but would be radically altered.

I wonder if they could manage to forget their past misery of losing all that they had and continue to move on? The above account is only one possibility... what if the first generation turned against itself in misery and dread? This people would be then doomed for sure. If they cannot forget, they will die out or at least live a miserable existence.

This presents a good analogy IMO for an individual life in which a person cannot forget past tragedies. If we don't forget and move on, we cease to care about our present and future situations. The desire to procreate may even diminish; that is, the procreation in thought and in physicality.