How Do Atheist Marry? And How Do They Procreate Too?

A lady on Facebook just asked "I'm still wondering how atheists marry". My reply was:

"Well, in the European Civil System, the two "marriages" (civil and religious) are separate. So they'd just skip the religious one, unless a Unitarian there let them in (they do allow atheist in their religion, you know). In the US, the two are one. So they would just go to a justice of the peace, as they are called. Or they could just cohabitate (as it's called in common law).

Um. So what is your question exactly?"