Yep supply and demand, and due to 30 years of abortion, there is a low supply of labor for the Amusement park industry and they have to import it from other countries.
I guess we shouldn't import oil to drive our cars using your logic.
I don't have any problem importing oil, if that is the result the market gives. Importing labor increases the TOTAL good, but primarily because it benefits the imported workers. It works to the disadvantage of workers who are already here, though, because it depresses wages.
My philosophy is that our responsibility is to American workers, not to Mexican workers.