Its very easy to blame others for faults in failures in a society or a community, and who is the easiest to blame? The outside. The immigrant. Having a hard time finding a job? An Immigrant took it. Taxes got raised? Immigrants leeching off support system. Neighborhood being changed? Thats cuz more immigrants are moving in. Crime rate going up? All these unchecked illegal immigrants.
I can't speak to European countries, but i'm not convinced that theres not much of a significant negative social or economic impact of even illegal immigration. Anyone against legal immigration is just a plain idiot.