A problem, when looking at the USA, is our perspective.
We are accustomed to the idea that lower levels of government can only do what Parliament allows them to do. In the USA lower levels of government can do what they like unless the Constitution, and constitutionally derived law, restricts it. The Supreme Court's primary role is to determine whether there is such restriction.
We consider the president of the USA to be the most powerful man on the planet. His actual, internal, political power is but a shadow of that of the UK prime minister.
As for religion, it seems to have become the practice of the president, at inauguration, to place his right hand on the Constitution and swear to uphold the Bible.
Sure, but the point is that the Supreme court have ruled that a ban on same sex marriage is unconstitutional so the states are required to fall into line, just as they have been in the past for similar equality based rulings where individual states had claimed the right to discriminate.
In the USA lower levels of government can do what they like unless the Constitution, and constitutionally derived law, restricts it.
Where do we disagree?
Oops - my mistake. Meant to post this in reply to Humph's comment that:
'The issue here is of the judicial branch of the federal government telling individual state governments what they can and cannot do. It goes beyond SSM.'
I think we are in agreement, recognising when the constitution, as interpreted by the Supreme court, may over-ride the normal primacy of the individual states. Humph seems to fail to understand this.