>You're assuming that only Christianity (and, in fact, only certain brands of Christianity) is a religion. Mormons are allowed more than one wife, even though most don't partake of that right, but it's there (unless they've changed the rules without telling me). Eastern religions also marry. Their marriages are based in religion, and they allow more than one wife.

Mormons can't marry more than 1 wife in the US. They agreed to stop that practice quite some time ago. You are agreeing with my points here, the laws are almost all rooted in religious doctrine.