In other words, they're doing to us what we did to them.
Nonsense. Mexico had a very tenuous claim to lands north of the Rio Grande at their best, and even that was only for a very short period - 1821 to 1836. At the height of Mexico's "occupation" of this area, there were only a few thousand Mexicans in the whole area from Louisiana to Arizona.
And - just as Mexico fought for and won independence from Spain, Texans fought for and won independence from Mexico (and the indigenous populations living there at the time).
Well, since we have now 10% of their people, I propose we just adjust the border south appropriately when we build our wall. After all, those people need a place to live.