Appeals to "survival of the fittest" piss me off, because they necessarily give up on the idea of improving society. I don't want to replace my ethics and hopes for the world with a barbaric version of pre-history. As a person who wouldn't be alive without corrective glasses and modern medicine, who also considers himself fairly productive, I'm might be a bit biased.

Besides, if you really want the end result of human nature, you'd just get what we have today. Humans are, overall, compassionate for fellow humans. It's why we tend to the sick. Hell, our compassionate nature is so strong we sympathize with sick or disabled animals.