The Grapes of Wrath is clearly a controversial novel that challenges predominant themes and ideas in contemporary American life, together with the time in which it was written. Two of these themes may be seen to be the relationship between economic freedom and individual happiness and the idea that the State is necessary in order to secure law and order. Each of these may be considered in turn.
The story of the Joad family is the story of a search for employment within capitalist conditions. Under these conditions, individuals are seen as being free, just as they under the American constitution and the general tenants of liberal democracy. In these circumstances, it is assumed that if an individual works hard and leads a blameless life then they may prosper. The Grapes of Wrath demonstrates that this is not the case, and in fact shows that modern systems of economic relations lead to exploitation and misery rather than to personal fulfilment. The Joads and others are forced off their land by the actions of banks and land-owners and are forced to work for increasingly lower wages in order to survive in the most base way. As such, the novel is likely to offend anyone who believes strongly that capitalist economics and liberal freedoms can guarantee happiness.
The novel also demonstrates that the State, rather than having a positive effect on society can be seen to be inherently harmful. This is shown especially in the difference between the two camps that the characters stay in and the relation between police. Towards the end of the novel, it is the actions of police that lead directly to social violence. This is an inversion of the usual belief that the State is necessary in order to ensure security. As such, not only is the novel likely to offend those how believe in the economic sanctity of capitalism, but also those who insist that its institutions work towards the social good and for the benefit of all.