Why does i government use religion as a basis on thing like gay marriage?

Unfortunately despite as much we want to believe otherwise religion is a part of politics on a personal level. However, lets look at this in a different way. What is politics? In general politics is about ideas on how a state should be run. However, what is religion? Is is not how we one should run our individual lives in a moral manner. So If one would come to the conclusion that incorporating religion as states moral guidelines it is not very surprising. This I guess means that because the two are both ideas on what could be arguably on very similar subjects it not surprising to see them blend together.