The government is right to discourage economic migrants coming in to keep wages low and fill low skilled jobs. A points based quota system can let us recruit talent and qualified people for higher paid roles. Whilst some firms and farms would like to have the benefit of more cheap labour we need to consider the strains this places on taxpayers. It also serves to keep low end wages down, hitting the incomes of those already settled here or born here in low paid jobs.
The EU once said that it costs a country about 250,000 Euros to provide all the capital it needs to welcome a new migrant. There is the cost of providing them with a home. There is the need for health capacity. If they have children we need extra school places. As numbers increase we need more transport capacity, more road space, more pipes and cables for utility supplies. It all comes to a big bill as we are all supported by huge sunk capital investment in an advanced country.
The best way of considering it is to see that if we invite in an additional 250,000 a year, each year we need to build the equivalent of an important new city to house them and support them. A new city costs many billions. Those are billions the employer of cheap labour does not have to take into account.
Rapid rates of inward migration also makes CO2 reduction much more difficult to achieve.