It sounds like you and the GP might be attaching different meanings to the word morality, perhaps? It seems like people use the word in a number of ways:
- 1) what every individual *ought* to do, independent of whether they actually do it or not (it sounds like this was the GP's meaning?)
2) actions individuals can take to further certain kinds of goals (commonly things like the well-being of other individuals or a group, personal fulfillment, etc.), with the desirability of those goals purely a matter of personal preference
3) things that individuals can be observed to actually do in certain situations (e.g. helping others), which could in theory vary just as widely as any other behavior
(Let me know if I'm missing a meaning... these are just the ones I can think of.)
It seems to me that the GP was using morality in the first sense. I don't have any real opinion on correlation between crime and religion, but it does seem like it would be hard to arrive at the first kind of morality without some kind of deity or authority figure to appeal to. While I disagree with a lot (most?) of what the GP said, it does seem impossible to me to start with a secular worldview and arrive at the first kind of morality - an absolute, "external" obligation or duty for an individual to behave a certain way regardless of their preferences or what they actually do.
I realize there are plenty of philosophers who would disagree, but I can't think of a way to elevate their positions beyond the level of pointing out that other individuals share similar preferences and/or behaviors. Since it seems like that doesn't rise to the level of a universal obligation to behave a certain way, it would appear that you're using the word "morality" to mean different things.