Why not offer Mexico State hood and absorb them into the United States?

With all the problems that has been caused by imagration, the fairness of living in this free country, why not? Mexicans would then be free to travel anywhere with in the United States, run and serve public office, go to public schools, live where they wanted to, work where they wanted to. They could turn in their green cards, get a social security card, work and pay taxes like the rest of us Proud Americans!