First off, just a bit of a nitpick, but as I understand it the Evangelical/pentecostal side of Christianity is doing pretty well, or at least it's not suffering from its members literally dying off (far from it, in fact). That was also my experience from about five to ten years ago.

Second, I'd argue it's way to early to conclude that abandoning religious moral guidance is a success. At most it's an (unprecedented?) experiment that so far seems to work.