Okay, your points seem very convoluted to me, but I think I've managed to pick up a thread to untangle this:
Mutual support and care were, surely, amongst the most important survival strategies which enabled the human species to flourish instead of becoming extinct hundreds of thousands of years before Christianity came on the scene.
Although this is never quite stated here, I think that the underlying problem with all your arguments is a
genetic fallacy:
1. Mutual support and care were amongst the most important survival strategies that enabled the human species to flourish, so they must enable our species to flourish
now.
2. A person who did not offer support to their group back then was left to their own devices, so that must mean that a person who does not support the group
today will be left alone to die in the wild.
When it comes to #1, it seems to me that you guys have associated support and care--two things that improved the individual's quality of life back then--with evolutionary success. So you must think that the evolutionary success of a species always provides a comfortable life to each member of the species. But this is patently false: there are many scenarios in which individuals lead miserable lives that increase the survivability of the group.
This is undeniable. Many other species have experienced this, and it's possible that we will soon be forced to give up certain comforts in order to survive as a species. Please, don't say that we are willing to give up comforts to see our children flourish, and that their future survival is actually a benefit to us. It may be true for some people, but many of us don't even plan to have children. Many of us just don't care whether the world explodes or not, as long as we live a happy, comfortable life while we are alive.
As a matter of fact, our ability to survive as a species could be much improved under a dystopic government, if we were willing to submit. We could grant people no individual rights whatsoever, and they would only do what improved our chances to survive as a society. You'll probably react against this, but that's only because you've already associated mutual care and support in a "feel good" way with the survival of the species. If all you care about is evolutionary success, then that's really the only reason for that reaction, and it happens to be a genetic fallacy.
Regarding #2, I'm sure you can see the absurdity of the situation. It's obviously not true that it's impossible to be a successful parasite in our society today. There are people who take advantage of others all the time and get away with it. You may say that's still immoral, but then you have to ask yourself why. Because it will harm society? Right, but why should an individual care that he or she is harming society? Oh, right, because an evolutionarily successful society makes our lives better. Oh, but wait, that was true back then, but not now...
There's no way around it. The interests of the individual are not always the same as the interests of the whole. In fact, if we are going to be rigorous here, we have say that there is no such a thing as the "interests of whole" at all. Evolution is not a guided process--it doesn't care whether a species survives or not. A species is not a conscious entity either, not in the same way an individual human being is, so it can't have any interests of its own. What we have here are some individuals who think it's pretty for their own species to survive, and who try to turn their own preferences into a moral standard. That's all there is to it.