The legal defense is that state's issue marriage licenses. Many states have formerly defined what marriage is in that states. A few have included homosexual unions as acceptable marital relationships. Others have restricted the definition only between one man and one woman. The legal defense is that a state and the citizens of that state have every right as a society, to define a social contract that is recognized by the law.You present define "Marriage" as being the same as "traditional marriage" which is defined as "between a man and a woman".
That doesn't mean that is any kind of legal defense.
So then why is it ok to say "this side of the restaurant (marriage) is for gay couples and straight couples. Now, all you other sexualities aren't even allowed inside." If the basis for argument is that it's wrong to disallow homosexual unions from marriage because it's unlawful define marriage as an exclusive thing for one sexuality, then why can't other sexualities along side homosexuality have the right to that contract? Defining spaces in a restaurant and setting the terms for a contract are very different. Suppose there is a contract set in place that gives financial benefits to corporations. Is it wrong for that contract to limit the contract only to corporations and not to individuals? The individuals have money too, they just aren't the same as a corporation. So is it wrong for to make contracts that only allow corporations or other entities? Is it wrong to any contract to have any boundaries? It isn't wrong for a state to define marriage, especially when the state's give out the licenses. They have every right to set the terms, conditions, and boundaries on the contract.If I define "Side A" of my resturant as "The White side of the resturant" and "Side B" of my resturant as "The black side of the resturant" I can't go "What? You can't ask me to allow black people into side A! That'd force me to change the definition of what Side A is!"
So then why is it ok to redefine something that has been legal for centuries? Why, within the years America has existed, have there not been any legal gay marriages up until this point in history? It's because society defines marriage, and society has traditionally held religious values.Having to change the definition of something is not a worth while legal defense.
Simply because something WAS defined in one way does not mean that is any kind of legal or constitutional standing to violate constitutional protections.
Sexuality is not the same as race. This is like comparing homosexuality to polygamy.The definition of "equality" as it applied to Black people at one time was "Seperate but equal". That definition was changed because it was unconstitutional.