I am an atheist, as such I was able to get married and I have both a wife and a son.
This is entirely consistent with the Constitution of the United States, as a person with no religious beliefs it remains entirely within the Constitution.
As a person ANYBODY should be allowed to get married, for any reason. Religious people, such as those just on NPR, may have a "problem" with this, but as religious people they have no right to be against it.
There has been marriage long before there was anything approaching Christianity, before people thought of themselves as Jewish. There was marriage in Greece, in Rome, in Japan, in China, in India. There was marriage everywhere.
Marriage belongs to all of us, and as long as the Government gives benefits to people for being married, it has long since moved past the "beliefs" of the relgious.