I consider Singer's argument to be the final word because I find no flaws in his logic. If you do, please tell.
I've made a few attempts to turn the discussion towards an understanding of morality and ethics and my ideas on this should be clear if you have been reading through. They are similar to the quote you dug up.
Keep the main idea in the forefront. I'll make a statement. Let's see what you think.
"Is it possible to act ethically without being religious"?
This is a direct response to the OP. My answer is yes.