The game has been explained and being prosocial is pretty much in your bones, so we also got help from the get go. Do you want a book that mentions MySpace and ketamine? The base is there, things can follow or not, not everything needed to be said nor could they have been without being massively confusing for anyone listening to the message presently. People who transgress greatly (all the pedos in American politics, for instance) do it not out of ignorance but because they simply don't care. Out of ignorance you might do something small, not rape or murder. It's not that the text wasn't available, it's not that they haven't heard what they should do or not do forever, this is evidenced by the way people who transgress greatly do it discreetly. They know, they just don't care. How to make people care? Actually believing in God's judgment is a way, believing in a non-negotiable encounter in which all your deeds are weighed and we all get what we deserve (and no confession or whatever religious trick could help you escape it). Idk other ways (no, recognising people die when they're killed or suffer when they're raped is not enough, else Kissinger and company would've been moral, lol, the is-ought problem remains a thing), and by default some will care more than others.
And on people justifying atrocities with their beliefs... I mean, sure, if you're a Paulian Trinitarian who believes belief and acts are fundamentally disconnected, and striving to be moral is not as important as "grace" and "understanding Jesus (a man) is God". Basically, if you take the tenets of Roman Catholicism and any offshoot seriously (and not, let's say, the TC and the Sermon on the Mount), I can see how one could say A and do B and still pretend they're more A than B. Only someone mentally off would think "oh but they said they were religious and believed in God" and take it seriously, lol. Come on, now, by their fruits you'll recognise them. But how do you justify atrocities as a Mosaic monotheist, for instance? How do you go on a Crusade, so not a defensive war but you're moving thousands of kms to murder and pillage? How? You can either go on a Crusade and not believe in God's laws and His judgement or you don't go but do believe, they cannot both coexist... because you know all of this is a one way ticket to hell and you'd have to be a maniac to understand hell as the most terrible thing ever and still choose to jump into it through your actions!
Finally, not all "religious texts" are made equally, even the Bible acknowledges their different authors, whilst the Qur'an is understood as a message from the Divine, recited by prophet Muhammad. One is a collection, an anthology, the other one is a singular book.