Onacruse:
The question you raise is actually an ancient one; one of the oldest in Western philosophy. The ancient Greek atomists and materialists (i.e. Democritus), the Sophists (i.e. Gorgias and Protagoras) and the Epicureans all dealt with the various ideas and notions that you mention in your post. There is, most likely no absolutely definitive answer, the reason being simply that there are no absolutes.
In a nutshell, what is (should be) the basis or foundation or our "morality"? Perhaps the answer lay in the etymology, the root meaning, of the words "morals" and "ethics." In point of fact, both are Greek words; "ethos" and "mores" both designate "customs." What is "moral" and what is "ethcial" has always been what is customary. Local customs and norms have always determined what is "ethical" and what is "moral." The ancient Greek sophists realized more than thousand years ago that what is accepted - even expected - in one place may well be absolutely forbidden and punishable in another place. As Protagoras said, "Man is the measure of all things."
Religious leaders and clergy of all faiths have consistently been hostile to materialism and related philosophical systems. In your post, you have raised an ancient "quarrel" that has been in the Western philosophical traditon for more than two millenia. The quarrel pits dogmatic founationalists against the relativists sceptics. It pits materialsits against theists.
I suppose that if you were to really insist upon an answer, I would say that you should conform to what is expected by the local community in which you live, your society. If you conform, things will go smoothly for you. If you break the norms, society will impose sanctions on you. What do you feel about this eventuality? Could you deal with the hassles? Would you be sadder, or happier, for facing society's wrath?