Then give them incentives to become US citizens! Why aren't we brain draining our competitors? We had the perfect setup to do so. Now we may be too unattractive and too long gone.
That said... there is a historical record of people complaining about Irish, Polish, Italian, Greek, and Spanish immigrants. Essentially every wave of immigration has been met with hostility.
So it seems the whole they are not X like us, is just an excuse.