"Sorry, Mrs. Smith, you are not entitled to be included on Mr. Smith's health insurance plan because you live in Florida now and you were married in Illinois. You see, we don't recognize Illinois marriages. But if you were married in Indiana, that would be a different story."
If you can tell me which states do not give people married in other states full marital priviledges in their own state, you might have a point. But you can't name one.
There have been numerous articles posted on FR over the years detailing why a constitutional amendment is needed to keep one state from imposing gay marriage on the other states. I suggest an FR search.
I am no scholar but I believe the following is the basis for each state recognizing marriages from other states.
Article IV of the US Constitution:
Section 1. Full faith and credit shall be given in each state to the public acts, records, and judicial proceedings of every other state. And the Congress may by general laws prescribe the manner in which such acts, records, and proceedings shall be proved, and the effect thereof.
Section 2. The citizens of each state shall be entitled to all privileges and immunities of citizens in the several states.
Only if that union meets the new state's legal defintion of marriage. For same-sex marriages, that is not the case:
STATES THAT PREVENT RECOGNITION OF OUT-OF-STATE SAME-SEX MARRIAGE LICENSE
As you can see, they include both Florida and Illinois.
In the South, the standard reply to the argument that (fill in the black) was legal in Massachusetts is:
"Well, you're not in Massachusetts anymore, boy, and it ain't legal here!"