Federalism refers to divided powers-ie making sure one group or branch of government does not wield too much power.
The states have specific duties and rights.
The federal government have certain duties and rights.
Some duties are shared-like defending innocent human life.
Every public official has a duty to defend innocent human life.
Defending human life is not a federalist issue. It is the business of all of humanity.
What’s that got to do with an amendment banning gay marriage?