Leviticus 20:13 Thou shalt not lie with mankind, as with womankind: it is abomination
Romans 1:27 And likewise also the men, leaving the natural use of the woman, burned in their lust one toward another; men with men working that which is shameful, and receiving in themselves that recompense of their error which was fitting.
And where does it say in the US Constitution that it's OK to make laws based on religious texts and beliefs?
The Constitution doesn't say it's OK, but it doesn't say it's not OK either. It only says Congress may not establish a religion, nor prohibit free exercise thereof. And that all powers not given to the United States, nor prohibited to the states, are reserved to the states, or to the people. So states can make such laws.
Many laws of the United States do take religion as their basis, but only because there is a common agreement. "Thou shalt not kill" is in the laws of Moses, but most people agree with it in general. The controversies arise because of disagreement on specifics, like the death penalty, euthanasia, abortion, and honor killing.
Marriage as a custom goes back at least 2000 years in the Roman Empire, before Christianity.
If your religion says that gay marriage or polgamy is OK, you can holler discrimination. Most people think polygamy is wrong. A majority think gay marriage is wrong.
Behold, it is written in the Book of Anne Southern:
1:1. A woman shall not do anything with another woman that she should do with her hubby with the doors closed, lest the neighbors think she is weird.
1:2. A man shall not do with another man what he does not do with Wifey because she shall find out about it and apply the Lorena Bobbit procedure -- with a dull cleaver!
1:3. A man shall not look lasciviously at another woman unless he wants to move up one octave in the choir.
1:4. A woman shall not cheat unless she desires to be shot.
1:5. Playing around either way before marriage shall result in both families poking shotguns in the kids backs and the preacher saying, "Are you people all out of your minds?"
If you're going to use Leviticus as reference as to why to ban gay relationships, then you also have to use Leviticus as a reference to ban other things it refers to, like eating pork and shellfish, and wearing mixed fibres. You can't pick and choose bits and pieces out of it to say what's ok and what's wrong; you either take it all, or none of it.
That being said, if same-sex marriage is banned because of what it says in Leviticus, then you should want to outlaw pork, in accordance with Leviticus. Not just the consumption of it (which would mean no more Christmas ham and no more bacon cheeseburgers) but also the handling of it, and also the consumption of shellfish (no more teriyaki shrimp and no more lobster tail). They are all an abomination to the Lord. It says so in Leviticus.
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