why do you think the defense of marriage act IS CONSTITUTIONAL?

Answer 1

There is only one constitutional argument that can be made to support it as being valid -- the specific wording of Article IV where it says "the Congress may by general Laws prescribe the Manner in which such Acts, Records and Proceedings shall be proved, and the Effect thereof."

Basically, the Constitution may give Congress the ability to do an end-run about the core intent of the Full Faith and Credit Clause -- by allowing Congress to declare the effect of such recognition to be nothing. But that's using a loophole to violate the basic principle of the clause.

The other grounds for parts of it being valid are that it originally referred only to federal benefits -- and Congress can set any limits for who gets federal benefits, as long as they don't violate the 14th Amendment.

An argument can be made that equal protection applies to gender-based discrimination, but the other argument is that even if it does, the DOMA meets intermediate scrutiny.

I personally think DOMA is an abomination, and nothing more than an enactment of hate-based prejudice. But an argument can be crafted that it is consitutional.