Then you can cite the part in article 1 section 8 that gives the feds any power over the institution of marriage, one way or the other?
I think that it would be more interesting for you to explain why the first decades of the founding Americans and all following generations were so anti-constitutional that they were defining what a legal widow is, for federal benefits.
Do you think that they were giving out widow pensions to homosexuals and lesbians and multiple wives?
I don't think that's the primary argument. Most people recognize the STATES' rights to define marriage according to local values and traditions without federal meddling. What happens in reality is that states which adopt a warped definition of marriage want to impose their skewed redefinition of marriage on EVERY OTHER STATE through Article IV, Section 1 of the Constitution, known as the "full faith and credit clause."
Full Faith and Credit shall be given in each State to the public Acts, Records, and judicial Proceedings of every other State.
That liber(al)tarian types like you cannot understand this very real danger seems to be a type of self delusion. Wake up.
Someone must officiate. And the obvious solution is provided in the second part of this section of Article 1:
And the Congress may by general Laws prescribe the Manner in which such Acts, Records and Proceedings shall be proved, and the Effect thereof.
THERE is the rationale for getting the federal government involved, not in DEFINING marriage that others must recognize, but in PROTECTING states rights to do so within their jurisdiction. Without DOMA we would now have NATIONWIDE recognition of the same-sex "marriage," along with all the Gaystapo nastiness that comes with it.