1) Because I do not completely understand the focus of your post, let me first deal with one claim which seems to be not covered by the title of the post:
ad issue 4: "Religious beliefs ..."
This statement seems to me either tautological or trivial. Nobody, neither religious nor a-religious denies this claim. But the perpetuation of a claim does not confirm its truth.
More general, religious belief perpetuates because it satisfies a psychic need of many people, e.g. see Kay, Aaron C. et al.: Religious Belief as Compensatory Control. Personality and Social Psychology Review 14(1). 2010, p. 37– 48
2) In order to focus the general term "religious belief" to the field of ethics, I consider the Jewish "Ten Commandments". Take Thou shalt not kill. One can easily argue for this rule without referring to any religious context. The rule serves to pacify and to stabilize society. That's the aim of each society.
The fact that there are so many exceptions related to killing external(!) enemies in war confirms, that the commandment aims at peace inside the society but does not proscribe killing in general.
Hence an atheist would argue: The commandment is not justified by a deity named Jahwe, but it is justified as a means to a generally accepted goal.
I agree with @virmaior that a theist would not accept that his religious believes on one hand are unjustified by his religion, but are justified on the other hand by their use for society. Instead he will emphasize that both is true: They are justified in a double way.