How is being against m immigration racist?

What I cannot understand is how the politicians and even our little gang of middle cl characters here with no experience of city life and the true horrors of immigrant ghettos now forming in UK is why do they revert to racist accusations when common sense says that immigration on this scale is social suicide and the British are busily building their own funeral pyres?My question is can someone say why racism starts being used to stop any debate or common sense argument?