Does it really need to be more complicated than this? History is history for a reason - you study from it, you learn about it in hopes that the mistakes of the past are not repeated. But you keep history where it belongs. For an illegal immigration wave to suddenly change into a movement to reclaim the American Southwest...what would these people do with the land? Would the Mexican government give it back to the natives who inhabited the land before the Spanish came? Likely not. They would use it against the US as a resource, just as we did the same thing.
Message to Mexico: Learn from your past mistakes and stop allowing druglords to rule your country. But most of all, keep your parasites OUT of MY country.