Polygamy was a federal issue. Utah was not allowed to join the union until they banned polygamy.
Liberals claimed we did not need a federal marriage amendment because we had a federal DOMA and state DOMAs and state amendments. Well the Supremes overturned the federal DOMA and federal courts have been overturning state DOMAs and amendments. Just because a few states have a temporary ok to keep their bans does not negate the states where bans have been overturned and whose appeal to the Supremes was declined.
We need a federal marriage amendment.
As it stood before this craziness, the differences between state marriage laws were very minor having to do with age and parental consent.
The Edmunds Tucker and related acts started this whole mess. Better to allow a tiny minority its religious right to marry, than lose a whole nation.