Why does Paddy chase Teresa's family out of town in the novel, The Thorn Birds?

Teresa is Meggie's close friend at the convent school in Wahine, New Zealand. When Meggie comes home with head lice in her beautiful red-gold hair, Paddy Cleary blames those "Dagos" and chases Teresa's family out of town. Paddy forbids Meggie to have friends outside the family from that point on.