What is, or is there, a non religious argument against same sex marriage?
Libertarian – The government has no business telling people who they can or can not marry, and should not be in the business of deciding who is and who is not married in the first place.
From the Obergefell opinion:
See Maynard v. Hill, 125 U. S. 190, 211. States have contributed to the fundamental character of marriage by placing it at the center of many facets of the legal and social order.
If states were to remove the centrality of marriage in social order, then possibly even after Obergefell there would be no protected right for SSM.