Amending a state constitution, like amending the Federal constitution, is not a straightforward task. Fred is a Federalist and he is acting as a Federalist. Let the state legislatures enact legislation properly defining 'marriage'. It can also be addressed on the Federal level, but Fred's Federalist beliefs rightly tell him this is the place to start.
“Like you I am confused by this new proposal. Why not let each state amend their state constitution to forbid state judges from interpreting that state’s constitution as requiring that gay marriage be allowed?”
For each state to amend their state constitution would take longer. My understanding of Fred’s proposal is that the Federal Court would mandate that State Courts could not overturn marriage as man & woman without the State Legislators voting for the overturn. This would put the decision in the hands of the people of each state where it should be.
Why not have one definition of marriage nationwide?