This is a really good point!
I was raised Jewish, with no idea of an afterlife, just with the commandment of Tikkun Olam: "heal the world." My partner grew up Christian and even though he no longer believes in an afterlife, he still fears death much more than I do.
I agree with you that when we get rid of the idea of an afterlife, our actions right now on Earth have a ton of import, because they are literally everything.
Great piece!