Originally Posted by TheDoc

It's because Mexicans think this land belongs to them... because the United States never lived up to its end of the bargain when the purchase/exchange was made for the land. This nulls the contract and gives the land back to the rightful owners, the Mexicans.

This is why they will take down American flag and toss it in the trashcan to put up a Mexico flag, they will fly it higher than an American flag as well, it's not just flown - it's flaunted at events.

It's a symbol of ownership, not of pride.