When politicians invoke fear of foreigners, they are presenting a cover story for a hidden agenda. (actually this is what happens any time a politician presents any idea, but i digress)
When it comes to immigration, the cover story is protection from foreigners, but the hidden agenda is control of the domestic population (and foreigners too).
Tighter ID controls means that cops can stop anyone without justification, this means immigrants and the domestic population. This also gives the government a pretense to spy..on EVERYONE. It also gives them a pretense to spend more money on law enforcement and border controls. And it allows them to KEEP PEOPLE IN if they want to flee the country with their wealth during times of confiscation.
This is just scratching the surface of how immigration policies are used against the domestic population.