In Part 2 I discussed the notion that the moral codes on which we actively collaborate are better suited to our way of life than those handed down from ancient times which are supposedly divinely inspired.
But why am I so certain that there is no deity giving us these moral mandates in the first place, you might ask. Well here's one more thing that I'm not saying when I say I'm an atheist: I'm not claiming to know with absolute certainty that there is no god or other supernatural entity in the universe. Maybe that sounds more like what you'd call agnosticism, but the fact of the matter is that the ideas of “atheism” and “agnosticism” are not mutually exclusive, and in fact most people who identify as atheists are also agnostics. The latter term is an acknowledgment that our knowledge of such matters will never be perfect. And at least in my case, it's an embracing of the logical methods of science as the best way to make statements about the nature of the universe. Science doesn't claim to know anything with absolute certainty, but its methods are the way to ensure that we're as close to the truth as is humanly possible. Science breaks a situation down to its constituent parts and makes sure we give each one due consideration before drawing any conclusions.