The trouble is how do you control illegal immigration from people who overstay their visas?
Many people come here with visas allowing them to stay in the country for a certain period of time (a few months, a year or whatever).
This may be to receive education here, or maybe they are sports people to come and compete here, or they are in entertainment industry and they come from say India or Pakistan (and other places) to perform here.
But what if they don't go home when their visa expires and just disappear into an area that is full of people from the same ethnic background.
I live near Birmingham and there are parts of the city that are virtually 100% Asian. All the school kids are Asian, and all the shops and restaurants and businesses are owned by Asians etc. A white person stands out like a sore thumb.
Suppose a person who overstays their visa goes and lives in this area?
How do you find them?, how do you root them out?.
You cant just knock on the door of every house.
It is a big problem and not easy to solve.