When you live in Sodom or Gomorrah, there's no point in standing up for your rights as a government employee.
Yes, “purged” is such an ugly word. I just can’t think of a pretty word for eliminating all Christians from government jobs. What word would you use?
Marriage precedes the very existence of the state, and is definable even lacking supernatural revelation. The foundational document of our Republic, the Declaration, wisely sources its authority on both God and Nature: "... and to assume among the powers of the earth, the separate and equal station to which the Laws of Nature and of Nature's God entitle them..."
Because God wrote His laws into our Nature, i.e. the simple fact that our species manifests binary sexual differentiation, and our reason tells us what this is for.