I group Agnostics, Humanists, Naturalists, and other similar groups under the banner of Atheism because while these groups have differences, they share in common zero reliance upon a religion revealed by God. This commonality unites them more than they know.
While an Agnostic might say, “It’s not that I foreclose on the possibility of a God, it’s just that for now I don’t see any evidence that he exists or has ever communicated with humankind.” That position is a little more defensible than asserting that God can’t possibly exist, however, practically speaking it isn’t very different from the Atheist position. This is because both the Agnostic and the Atheist will still live their lives as if there is no God and will rely on their own reasoning without being disposed to consider what God might think about their actions.
Ultimately, by not thinking to heed some higher, eternal order, all of these groups end up living their lives and making up their political/social minds as if there were no God. This is why I argue that post-modern non-religionism will lead to the same logical conclusions as post-modern Atheism.