I do not believe anyone is demonizing Mexican immigrants.  The problem is not Mexican immigrants.  The issue is "illegal aliens" and these are people who are breaking the law of our land.  They may be Mexican and they may be of other nationalities.
 
In the scripture you quoted, the "strangers" in the land were being assimilated into the culture of the nation.  In the situation of the "illegal aliens", they refuse to be assimilated into our culture.
 
Another problem with the "illegal alien" and our porous borders is the ability of Islamic terrorists to move across the border and to smuggle in their weapons without being detected by the authorities.
 
I just do not see a parallel here.