Why does Jem destroy Mrs. Dubose' camellia bushes?

Mrs. Dubose regularly hurls insults at Scout and Jem. Although the children do their best to ignore her, one insult pushes Jem over the edge. She attacks Atticus for defending Tom Robinson in the worst way, "Your father's no better than the niggers and trash he works for. " This pushes Jem to cut down her flowers.