God and His law always has to be the basis of a free society; only He is present in the darkness away from the sight of others when you are sorely tempted and know you will never get caught.
But even for believers, when the original sin of the body's inbuilt demand for personal survival, from which all sins against others springs, I believe, there must be the enlightened use of the survival firmware.
I've seen, and am seeing, as much and more destructive results from attempts to be altruistic in the face of the foundation of original sinful nature - to survive at all costs - than I do from firm selfishness with respect for others' self-interest.
When working a business deal, I trust self-interest before I trust expressed motivations to do me good at the expense of the doer.
Yes, certainly, put in those terms. Economics is, and should be, driven by self interest—or by interest in providing for one’s family, or donating to charity. But donations should be free.
It is precisely the problem that “altruism” as it has appeared since the eighteenth century has no real underpinnings, except religion. So it can include all sorts of false or faulty versions. Or it can be used by Communist apparatchiks as a way of concealing their own drive for power.
Aristotle was able to define moral behavior reasonably by his theory of the virtues, but he was likely a religious man, who believed in a God who was First Mover. So it can be done by philosophy, but for most people it needs the appeal of religion to make it worth pursuing.
What you are criticizing is varieties of false, mistaken, delusional, or opportunistic altruisms, of which the welfare state is one example. I don’t think we disagree about that. But it’s part of why a purely rationalistic altruism won’t work, any more than purely rationalistic selfishness will work.