Studies that show a positive effect of immigration on the economy are deeply flawed in that they take no account of the use of capital infrastructure and services that have funded by the indigenous population. When you say that the government (i.e. you and me) haven't invested in services and infrastructure to meet the increased population this rather proves my point. To have any chance of accommodating all these extra expel we would need to spend far more than they will ever generate in taxes. Let me put it this way, if the population increases by 10% then we need at least 10% more housing, water, electricity, gas, roads, schools, surgeries, hospitals, doctors, nurses, police... the list goes on and on.