There are always going to be jobs at the bottom of the chain that the native, dead end movers aren’t going to want to do. At least not for the wage that it’s worth.
Immigrants have always filled those jobs. For example my sainted forebears were unskilled, Catholic laborers in Belfast. The job market was let’s say less than rosy. Even being a mule in the coal mines for low wages was better than that. Not enough native dead enders wanted to do it. They did because bad as it was it was an opportunity, albeit normally with an early death from an accident or black lung. Not much difference with these guys coming up from the south. They take the jobs that our unskilled don’t want or won’t do. Because it’s still an opportunity for them.