One key statement by the Court notes: 'DOMA singles out [a] class of persons deemed by [the] State entitled to recognition and protection to enhance their own liberty'...
You have to accept the class struggle premise of the decision to agree with the ruling.
"On an issue as sensitive as this, knowing that Americans hold a wide range of views based on deeply held beliefs, maintaining our nation’s commitment to religious freedom is also vital. How religious institutions define and consecrate marriage has always been up to those institutions. Nothing about this decision – which applies only to civil marriages – changes that."
Religious freedom is impinged upon with this legal re-definition of marriage and Obama is not daft; he knows this is a blow against centuries-old Judeo-Christian ideas. Even the promiscuous Greeks and Romans would not have been so foolhardy as to disparage a central social institution such as a marriage between a man and a woman.