Some countries literally are shitholes

[The Grand Nudger]

All intentional asshattery aside, there's a tendency for the recently enfranchised or recently naturalized, realizing the value of the thing they now possess, to close the door behind themselves, so to speak.  It's easy to see why irish and italian immigrants, or the children of either..would not want to have to compete with future waves of immigrants or other minorities for jobs (or recognition).  In that way the newly white closed the door on all the "non-whites" - and even immigrants from their own countries of origin.  Irish american natives were famously dismissive of irish immigrants.  Perhaps moreso than most.  

Today, there's a certain subset of people outspoken for african-american causes (and also racist pieces of shit that use it as cover - granted) that think we might want to get our shit together on that front before we spend too much time worrying about making life better for the undocumented.  A gallup poll that broke down concern by ethnicity showed that, as a group, black americans were the least concerned with immigrant issues.  In the middle (barely) where non-hispanic whites..offset perhaps by the fact that at least some of those saying they were concerned -probably- meant that they were concerned about all the mexicans being here...and ofc the group that expressed the most concern, no surprise, being hispanics themselves.  

Even there, though, you can find the rhetoric of a closed door.  Mexicans and cubans..for example, not necessarily fond of being mistaken for each other..or each other, and enfranchised people of hispanic descent greatly resenting being lumped in with whatever portion of the undocumented demographic is said or maintained by Some People™ to be giving the rest of them a bad name.

@Tiz
That scam you briefly described above -still- fuckin works, too..only now it's used to set the poor against each other, by and large....though I guess we could say it was always thus. Nothing new under the sun, eh?