I think people maybe have a rose tinted view of what Britain was like in the past and that if we had more of a monocultural like in the past then the good old days would come back.

Spoiler though - there were no “good old days”.

Infant mortality was 10 times what it is now.
People died of TB in their thousands.
Real poverty was widespread.
Children were battered senseless at home and in schools.
World Wars occurred.
Nuclear weapons were dropped.
People had to have surgery without anaesthetic.
Huge swathes of the population had little to no education.
Crime rates were through the roof.

I could go on and on and on.

The good old days were really pretty shite.