Why are the "travellers" persecuted in the story, Cat, Herself?

The travellers find themselves the object of a fair amount of persecution, partly because they believe that no one can own the land and that they are entitled to any game they can catch. They are often forced to move on by local authorities, such as Sergeant McKendrick and Constable Miller. Their children are sometimes mistreated in school and, towards the end of the novel, firebombs destroy their campsite, killing Alec's mother, Isobel's baby, and Cat's dog, Shuffler.