Because that wouldn't hurt vulnerable minorities in particular. It's the old fascist technique of feeding people scapegoats on whom they can blame their troubles and take out their anger and frustration, so that they never ask whether the government might be responsible for their problems. It works best if you victimize a minority group that most people are unfamiliar with, and make it dangerous for people of that group to show their faces in public. Then the masses will never learn that they are not to be feared and hated.

Unfortunately the British people are staggeringly easy to convince that the government of the last 14 years has nothing to do with their declining quality of life over the last 14 years. It makes this scapegoating propaganda all too easy.