Here’s what I have discovered just by moving through life and trying to pay attention: People who are adamantly religious generally change over time by switching to another religion, becoming an atheist, becoming more delusional, losing interest in their religion, and/or finding new ways to interpret their scriptures and teachings. This means they are highly unstable, especially when they are young and wont to place all things in a neat and tidy box of idealism. People in their teens, 20s, and 30s tend toward idealism and are feeling around for their place in this big, scary world. They have decades ahead of them, if intellectually curious, to explore new ideas, philosophies, and their own inclinations and attitudes.
The idea of morality is a very strange one. Why are people, especially religious people, so hung up on trying to prove that it comes from a god that was clearly invented? Because this god and the religions of mankind offers a means of ordering a world that seems so out of control and frightening. How certain and stable is the religious person’s trust in their god if they constantly have to be his spokesperson and defender?
Holdsworth’s dichotomy begins with a logical fallacy when it proposes “I want to start by setting the stage between two alternatives…” This limits the possibility of answers other than the two created in the mind of the arguer. Just because you say “there are only two choices” doesn’t mean it is so.
I applaud you for jumping into this well-worn pit of limited thinking. I think you capsulized your argument in this well-constructed argument: “…when we add evolutionary biology, cognitive science, sociology, and so forth to the mix, morality no longer seems so baffling.”