Any administration has the right not to argue for a law, for DOMA violates the Equal Protection Clause of the Fourteenth Amendment (granting marriage rights to some adults but not others). It also has the right to argue against a law, or in the case of the Bush administration, the Constitution as in the Fifth Amendment right to habeas corpus. In this case, defending this crap law is NOT in the interests of America as a majority of Americans (via numerous polls) approve of same-sex marriage and it would be defending a law that runs counter to the Constitution..