[Luis Gonzalez]

Here's a better take.

Once this Amendment is ratified, would a State be able to exercise its Constitutional right to define marriage?

No.

[Snuffington]

Once this Amendment is ratified, would a State be able to exercise its Constitutional right to define marriage?

And once the 18th amendment was ratified, a state was no longer able to exercise its Constitutional right to define whether "intoxicating liquors" would be available for sale in their jurisdiction.

And when the Constitution itself was ratified, the Second Amendment prevented a state from exercising its Constitutional right to prevent private posession of firearms.

This is argument by definition.

[The Iguana]

Once this Amendment is ratified, would a State be able to exercise its Constitutional right to define marriage?

My money is that this Court would now argue that states can't do so now.

And it is only a matter of (little) time before the Court starts getting appeals the moment one state (most likely by judicial fiat) recognizes gay marriage.

Gay groups are not trying to get their way through the Democratic process. They're doing it through the ukase of the courts.