Why the hell would anyone be against immigration or in favor of enthic cleansing?

A large number of people coming in all applying for the same jobs, thus depressing wages. Whilst at the same time creating a larger demand for houses, raising the price of houses. And a more diverse workplace makes the workforce less likely to unionize, thus reducing the chances of successfully campaigning for higher wages. And because everyone is so different, loyalties to different nations, religions etc no would be able to agree on where their tax money is wasted, no one would have much care to look after their community. You'd be creating one big slave plantation.