The issue is whether a nation should be allowed to control entry over its borders. Most other countries do. We do not. Some think that is OK. Some think it will lead to tension and unrest. It is an issue.

Consider population density. How many countries have a higher one? this leads to pressure on resources such as housing. We have a housing crisis. Ordinary workers can not afford homes.

We have to make special provisions for nurses, teachers and firefighters or we would have none in our towns. ordinary workers are stuffed.

Assylum seekers have to be provided with homes and so are placed before others in the provision of social housing. I am not saying this is wrong, just that it inevitably causes tensions.

Most countries arrest illegal immigrants. We do not anymore. Recently near Hertford a number were caught when they ran from a van. The police gave them the fare to go to a reception centre and sent them on their way. I'm not saying that is wrong, but others do it differently.
I have heard some British people describe their experience in USA when they were found to have minor Visa infringements. They were held IN CHAINS for over 24 hours and then expelled.

There are different ways of dealing with immigration. Is it not an issue that can be discussed?