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.