To Kill a Mockingbirdcould very well serve as a study in social dynamics considering the way in which Harper Lee cleverly brings out the class categorization that occurs even in such as small town as it is Maycomb. Lee lets the reader into the daily interactions of small town people and how they divide themselves into groups based on intellect, race, religion, and even by the history of the family in that particular area. Far from fiction, this is a microcosmic fragment of what Nell Harper Lee, herself, saw occurring in rural Alabama as a child growing up there.
Chapter 23 illustrates this rural classicism with clear detail: Atticus explains to Scout and Jem how, in the court system, the word of a white man automatically supersedes that of a black man. He also explains that it is a member of the Cunningham clan who has actually shown support for Tom Robinson. As a result, Scout leaves behind her former dislike for the Cunninghams only to be told by her aunt Alexandra that "the Finches do not mingle with trash like the Cunninghams". This illustrates how Alexandra looks down on the Cunninghams while the Cunninghams look down on the Ewells. It is also described then that whites look down on blacks, and that the latter are at the bottom of the system. However, there is more to it than mere color and race.
The Ewells are actually the clan that belongs to the lowest, most degrading, and less sociable stratum of Maycomb society: they are what is colloquially referred to as "trash", precisely because their living conditions and social attitudes are disgusting, immoral, unhealthy, and chaotic. When Mayella Ewell falsely accuses Tom Robinson of rape, the typical social ranking system is put to the test: the Ewells are white, but they are barbarians; would their word still supersede that of Tom Robinson, simply because he is black?
Being put in the spotlight as "victims", the Ewells' enjoy their only chance to look down upon someone, namely, a black man like Tom. Although they know that they are blatantly lying, the Ewells also know the system and how to bend it. They know what they are, what they do, and how nasty they are behaving. Having the power to put down someone is still power to be had. This is why Ewell is adamant in proclaiming his hatred towards black people: because this is the only chance in his life where he can turn the table and say that it is he who hates, and that it is they who are victimized.
This is the typical behavior of someone with no dignity, character, nor self-respect. Therefore, is more than likely the course of action that an Ewell would take.