---Faulty premises can lead to faulty conclusions.
Society offers greater protection (hence increased opportunities for survival) than living outside of a civilized society with its human construct morality. Loving one's neighbor as oneself is fundamental to that increased protection. Your premise that "survival of the fittest" is the opposite of "love your neighbor as yourself is not justified.---
Why does society offer better chances of survival?
Why don't cougars form such societies?
The pooling of resources. The division of labor. Does that help. By banding together, instead of fighting amongst ourselves, we are able to fend off the cougar attacks, while others in the society can plant food, harvest food, go on a hunt, women can raise their children in relative safety, etc., etc.
Why don't cougars form such societies?
Simple. They haven't evolved far enough to understand those implications. Many other breeds of animals have, however, figured that out.
Our original morphology put us in a situation where predators found us easy prey unless we banded together for protection. That same morphology also put us into a situation where protein was very difficult to obtain unless a number of members cooperated in hunting.
"Why don't cougars form such societies?
Why do zebra, horses, elk, and any of a number of other organisms form societies? Evolutionary paths are contingent on current state. The direction animals take in forming societies depends on environment, co-evolutionary organisms, current morphology, weather, and the luck of the draw.