I think that a bunch of basic social functions started out as religious and are now carried out by atheists and the like (marriages, potlatches, etc.). In a pre-scientific world, everything was religious. What is a church but community and religion? If we can strip the religion from marriage, why not church? I know atheists who attend Unitarian Universalist churches for the community (and my parents took me as a kid, my dad an atheist and my mom a mushy-not-really-religious-but-believes-in-somethingist). It's not for me, but that's probably a social issue related to how I respond to those sorts of groups and not really related to religion. Secular churches do exist.