Both are subject to hatred due to being born as something socially unacceptable. The Ewell
family have been 'the disgrace of Maycomb for 3 generations' and Tom was born a black
man in the 1930's- a time in which racism was common and was seen as normal and
acceptable.
Tom and Bob have an existence in the minds of Maycomb's populace that extends far beyond what
they are as individuals in reality. As a Ewell, Bob Is regarded as foul, unhygienic and vulgar, and as a
black man, Tom is considered beneath whites- they're both widely thought of as scum.
We hear lots ABOUT both- but not much from them.
They both have SOME conception of what they are to society- although
Bob is such a vulgar character, he's still put above Tom because he's
white.