I think, to be thorough, I should discuss Buddhism today. I've gone into several of the other world religions. Let's consider a few of Buddhism's basic tenets, and the social usefulness and survival value of those tenets. At least, a few of them. Like Christianity, Islam, and so on, Buddhism contains many sects. I can't begin to discuss the full gamut of those sects here. Let's just focus on a few concepts that are salient from this social usefulness perspective. 

Buddha aimed to help his fellow humans to stop suffering. The key to doing this is to give them the tools, that is the concepts, to see that it is their wishing and yearning for things beyond their immediate awareness that is making them suffer. You don't need those things that you yearn for. If you could have them they wouldn't make you happy. You need to stop yearning. Be fully here and now. The moment is beautiful and much more than good enough. 

To do this you need to see and experience the oneness of all of the universe. As the old joke goes, Buddha walked into a pizza shop and told the person at the counter, "Make me one with everything." All of our thought processes depend on concepts that in the end are illusions. There are no things made of matter and things not made of matter. No women versus men. No food versus poison, no future versus past. There is only here/now. Even thinking you are separate from everything you see is an illusion. Get over that, and your suffering will stop. End dualisms of every kind. Touch nirvana, the unimaginable. 

It has worked at a basic functional level for millions of people for thousands of years. Whether the historical Buddha really existed or not, the idea has great power. It can make life, even a very hard life, bearable for people who truly believe. They can even spend their mental energy concentrating on doing each task or movement in their day as beautifully as they can. In the humblest of lives, there can be beauty. Pumping water. Planting crops. Nursing a baby. Digging an irrigation ditch. Even typing on a computer screen. Buddhists tend to make good, hard-working, law-abiding citizens, which boosts the efficiency of the larger society.  

There have been abuses and errors committed by Buddhists too, however. They tend to illustrate how in the real world, people of different belief systems, including Buddhists, end up confronting one another and fighting even when both sides will tell you that they were doing their best to avoid that exact situation. The people of Sri Lanka are in large majority Buddhist. But they did some nasty things to women and children of the Tamil sect nevertheless. Just one example.  

But these failures are not what worries me about Buddhism. What does worry me is whether people who think the reality they are seeing is all illusion will be able to recognize and stand up to those who would turn them into slaves. Or to go even further, I wonder why Buddhists would bother to have families and try to provide for them. That seems irrational if they hold the contemplative life in more esteem than they do the active, involved, worldly one. 

Involved, caring people have made many mistakes down through history, but I believe they do in the end tend to be the ones who learn lessons from experience and take measures to right the mistakes of the past. 

We as a species can't live contemplatively anymore. The hazards facing us have just gotten too dangerous. I have to care. I have to try. I can't just watch the universe roll by and smile. Nor, I believe, can the vast majority of the human race if the vast majority of the human race is going to survive. 

But I do admire their philosophy. It is subtle, gentle, and profound. And once in a while, I really do see not just trees, but trees against the sky.