Can you provide some examples of safe and prosperous secular societies? The main ones that come to mind are communist countries which haven't fared too well historically.

Also what do you mean by justifying what we would have already done? Do you mean if we didn't have a 2,000+ year Judeo-Christian tradition that we'd have the same morality? There are a lot of ideas that ethical monotheism introduced that were completely alien at the time so this seems unlikely.