I am both an atheist and a strong proponent of individualism without disagreeing with your comments on how this naturally comes with responsibility, more than many spiritual constructs do where you can pass some of your responsibility to a third party such as fate or God or karma. Collectivism is a shared brain, individualism is a hivemind.
To not believe in an afterlife is also a belief. We cannot know. The truth is we don’t know.
> Being religious doesn't intrinsically make one more or less collectivist or individualist, it all depends on the philosophy of the religion (or non-religion).