In Song of Solomon, what was the significance of Macon Dead’s death to the other “young boys at the time”?

In order to answer this question, I will ground our discussion in Chapter 10, which appears in Part II of the Toni Morrison's novel. During his visit to Reverend Cooper's house in Pennsylvania, Milkman learns the story of his grandfather's murder. Jake "Macon" Dead was killed by white men who were never prosecuted for their crimes. Astonished that no justice was ever served, Milkman interrogates the Reverend to figure out why his grandfather's killers faced no punishment.
The Reverend, in his wisdom, tells Milkman an anecdote about how he wound up with a knot the size of a walnut after attending an Armistice Day march in Philadelphia after the end of World War One. Because the white people in the city did not want blacks included in the march, the police were called. They actually trampled the black marchers with their horses in order to drive them away.
This anecdote is intended to suggest that white people, as a general rule, can not be expected to uphold the rules of law and order when a black person is the victim of a crime or injustice. Therefore, it becomes clear that Jake "Macon" Dead's death was so significant to the young people at the time, Reverend Cooper included: because it showed them this ugly reality of their powerlessness against violence and discrimination.
Milkman even refers to his grandfather's murder as the "beginning of [the young boys's] own dying," suggesting that from that moment on, the boys understood their own mortality; if someone as strong and dignified as Jake "Macon" Dead could be killed without retribution, then any one of the young boys could be, too.