They’re both right!
I support an Amendment banning it, but until there is one Constitutionally it is a States’ Rights issue.
Sidebar: Personally I don’t think the .gov should be involved in marriage at all as that is really a religious institution.
Congress has the authority to dictate to what extent, if any, various judicial actions in one state are enforceable upon another. I see no reason this wouldn't give Congress the authority to declare that no state shall be required to honor any marriage which does not involve precisely one male and one female.