The bill of Rights was written simplistic for a reason, my friend. So regular folk could understand their rights without a lawyer.
This was my assessment, in steps:
1. Marriage exists because it's a religious ceremony for Christians.
2. The government got involved and gives religious marriage authorization, certification, and tax discounts. (unconstitutionally, see amendment one: government can make no law regarding religion or preventing The practice)
3. Any person can follow any religion in America (as long as it doesn't violate other human's rights.)
4. Create a new religion that allows gay marriage.
5. ???
6. Profit.
Allowing people to marry should and is protected under the first amendment. The Bill of Rights wasn't written in short, easy descriptions so that we could conflate meaning and exclude people of their rights. The truth is exactly opposite of that!