Federal mandates on how states regulate insurance would violate the Tenth Amendment:
"The powers not delegated to the United States by the Constitution, nor prohibited by it to the States, are reserved to the States respectively, or to the people."
The federal government telling you, as an individual, that you MUST buy health insurance violates that same amendment plus the Ninth Amendment:
"The enumeration in the Constitution, of certain rights, shall not be construed to deny or disparage others retained by the people."
So why can't YOU PEOPLE follow your own Constitution????
There's no need for such an amendment