It has nothing to do with unskilled labor anymore. Where I work they are putting illegals into skilled positions (even though they can't communicate). It's about the money. A roll tender used to make about $15/hr. but the hispanics will do it for $10.
What's wrong with buying something cheaper when you can? Don't you do that? And if you do, then why do you deprive the owners of the company --- people who gave the hob in the first place and without whom you would not have any --- why do you deny them the same right?