(federal government lacks a rational basis for denying federal benefits to homosexual couples and, as such, Section 3 of the Defense of Marriage Act violates the due process clause of the Fifth Amendment; homosexual couples should be allowed to file joint income tax returns; court rules that Congress has no rational interest in promoting morality and conserving limited resources; court rules that, for purposes of federal tax benefits, federal government bound by state law - as such, opinion lays groundwork for basis of claim that recently enacted health care mandate is unconstitutional).