Automation, Globalisation and population growth have already made most Woking Class and lower Middle-Class families poorer. Fewer job opportunities and lower wages are already the trends for most people. The widening gap between rich and poor is growing because the rich know that by reducing Labour costs, they increase profits.
Importing more low skilled into a First World country makes the situation worse. Importing people with a culture of having larger families makes it far worse.
No longer does more people equal more jobs. Factories are automating or leaving, any growth in GDP will be enjoyed by the upper classes. We already know it doesn't trickle down.
It's better to give money to a family in a Third World slum where they can live on $1,000 a year than importing them into a country where they need $10,000 to live. The problem is the former policy doesn't make the 1% richer.
Today you might enjoy getting your garden looked after cheaper by migrants. How long before their children are competing with your children for the same job and one is willing to take lower wages? Leaving one unemployed and the other paying higher taxes to support him.