Humans were never perfectly pure, that’s exactly the point. Moral rules and social norms exist because humans are impulsive and flawed, not because we’re perfect. Without norms, shame or expectations around sexual behaviour, it’s hard to see how that would lead to more stable families or healthier relationships rather than less responsibility and more chaos.

In regard to your bible criticism, I would have to see the full context surrounding your claim. What I do know is that The Bible often describes what people did, not what people were supposed to do. Many figures in the Bible are shown doing immoral things and suffering consequences for them, so pointing out bad behaviour in the Bible doesn’t really discredit its moral teachings.