In "To Kill a Mockingbird," why does the mob want to lynch Tom?

The mob wants to lynch Tom because to them, Tom represents a threat to their segregated way of life. Tom has been arrested for raping Mayella Ewell, the worst thing a Black man could do. Rape of a white woman by a black man challenges the idea of segregation and separation of the races at a very basic level. The mob opposes Tom both because he is black and also for his supposed actions. However, because of Scout's actions of singling out Walter Cunningham, the reader sees that this mob is really composed of people who would act differently as individuals. Scout realizes this, too, and is able to defeat the cowardly ways of the mob by reminding them of their individuality and responsibility.