Marriage is based on the laws of nature which are immutable. Way before any church doctrines.
Man, woman, babies - natural law.
Two men, anuses, or two women, licking, implements - etc - unnatural!
Sheesh, use your brain!
The Creator created marriage. The church, as his instrument in the world, enforces his will.
The rest of your post is not worthy of response as it has nothing to do with the argument of what marriage is and whether government should be defining it!