Yes, the distribution of wealth is an uneven playing field but a lot of the time, the poor are poor because of the choices they made.   Mexico could have had many of our economic advantages if they had made different choices.  They have many of the same mineral and other resources that we have.   They have good spots for tourists.  They have crops that we have a hard time growing here.
Also if it is not government policy to  be encouraging the people to come here, why are they so intent on stopping Trump's wall that they train their nationals to become US citizens?