This movie challenges the stereotypes, the presumptions, the "little boxes" that we are so eager to put each other in to fit our world narratives.
As a viewer, you are put into this position right from the start; waiting for the presumably hostile little white town to turn against the newcomers, only to realise that they are the ones who have brought with them all the snobbish, elitist, ready-to-be-insulted egos and attitudes (e.g. the father is insulted when he thinks he is corrected for not knowing what the word 'marked' means; the professor talks about her 'smart and amazing New York friends' when she is drunk; the father is angered when he believes that his kid is being falsely accused just because he is black and so on).
The beautiful house that hides mold beneath its walls symbolises this externally perfect family that is forced to recognise their own inconsistencies and fallacies. Both the parents do not put into action what they preach with their books, lectures and intellect. They are trying to teach their son what is the right thing to do, but not through becoming role models themselves, just through empty words. This is why the dialogues are so stiff and awkward to the ear.
Still, the family realises this and they try to start fresh: the child running behind the truck yelling 'we are not bad people'.
Yes, we are not bad people. We all make assumptions about others without knowing anything about them. In the end, It is not the place that is 'wrong', it is our own perceptions holding us back. And sometimes, our self-stigmatisation.