I believe if someone loves another person it should not matter the sex. I do see problems of people using it as a loophole to get citizenships. But if I loved a man and was unable to marry him he would have no access to my last wishes or my assets if something were to happen to me.
"The powers not delegated to the United States by the Constitution, nor prohibited by it to the States, are reserved to the States respectively, or to the people." - The Tenth Ammendment.
The issue of gay marriage, according to the constitution, should beleft to the states to whom it properly belongs.