Atticus says that the Ewells are people of disrepute, who have been so for generations, which implies that their lifestyle has become a custom. He further avers that they cannot be changed or displaced, for they would not fit in a normal, decent society - they are uncivilized and would never adjust. They reject education and only use it as a means to an end - since they live in abject poverty, they receive a social grant from the state, as long as the children are registered for school.

Atticus is furthermore of the opinion that they live like animals. The Ewells live in absolute squalor and filth. They are looked down upon by the rest of the inhabitants of Maycomb. Everyone ignores them and no one does anything about their criminal activities. In this sense then, they are privileged. Since they are white, it seems, their crimes are ignored - an indication of the injustice of racial profiling and disparity at the time.

Atticus is a decent and well-respected citizen and he wishes to instill in Scout the morals and values that would make her a respected member of society. It is therefore obvious that he wishes her to 'see the other side' as it were, so that she can make appropriate value judgements.

How does Atticus explain the Ewell family?

Atticus is the most understanding character in the novel. Therefore, his perspective on people and events differs from that of other people. When he describes the Ewells to Scout, his words are a model of tact, truth, and compassion.

He basically says that the Ewells are in a special category, and so the normal rules that apply to other people do not apply to them. The reason for this is because Bob Ewell, the head of the Ewells, is a drunk, who does not take care of his family. Moreover, Bob won't change. Therefore, if people tried to enforce laws and rules upon Bob, then his family would suffer greatly. 

Atticus says that all people know this, and so they allow the Ewells to bend and break the rules out of compassion.