Problem:
While trade agreements are not designed to better the lot of the poor and disadvantaged, they actually CAN have that effect from what I can see. BusinessWeek had a cover story about Africa a few years ago titled "Can Greed Save Africa?"
(https://www.businessweek.com/stories/2007-11-28/can-greed-save-africa).
The point was that foreign direct investment has an immediate and dramatic effect on economic development and the economic condition of the African people. The impact of this "greed" on the economic welfare of the average African has been far greater than the impact of decades of "Save the Children" and other charitable efforts.
In trying to make money, the U.S. multinationals are indirectly improving the living standards of their Mexican work force.
I think it can be argued that NAFTA has produced significant net benefits for Mexican work force. NAFTA creates an enlarged production base in Mexico. As low-income jobs move from Canada and the United States to Mexico, the Mexican economy strengthens giving Mexico the ability to purchase higher-cost American products. The net effect Mexico increasing its imports of high quality American goods is positive for the American economy as well. As more and more Mexicans move towards the middle class, they and their children will have the opportunity to move up in life.