Point taken, but they keep coming. It they were told that with a vote they could come here without border hastles what would they do? And don't forget all those people who have never tried to rush the border would believe they would be qualified for welfare where they are. It would be a lot like the reunification of Germany. Lots of problems, lots of costs but they did it.
That said, I am certain the problems associated with statehood for the nation of Mexico would not be minimal.