In the last line of Angry Black White Boy, it says that Macon joins his ancestors. It never explains who these ancestors are, but there are a few explanations which make sense.
The first of these explanations is that the ancestors are referring to Macon's parents, grandparents, and Cap Ansen. The line would be saying that Macon is joining those before him who either actively participated in racism or ignored it. Macon views all of these people as really bad because even though they may recognize the problem, they don't do anything to fix it. Instead, they just go on with their lives accepting their white privilege and staying happy by remaining ignorant. At the end of the book Macon also wants to return to this state of mind. This interpretation would also make sense as Macon writes "cap" on the bus which shows how he thinks he is getting closer to both Cap Ansen and the Cap that was hated by every member of the graffiti community. Even though he was involved in graffiti culture, comparing himself to one of the most hated just shows how much Macon is struggling with himself right now.
Another interpretation is that the ancestors are referring to the other people like Macon, white people who found the problem of race in America disturbing and wanted to change it. Macon is sort of unique in his approach because he educates himself through hip-hop and takes a very militant viewpoint, but others have come before him. If we take ancestors to mean this, then when Macon fails he is being compared to all of the other whites who sympathized with the cause who also failed. There have been white people who supported the cause and were fairly successful, like the Jewish man in the book, but no one like Macon, who wants to change how white people evaluate racism in America, has ever really gotten anywhere.
Macon's death makes us question why he is being killed. Is it because he is not identifying with his white ancestors, or is it because he is identifying with those who have tried to change the mindset of white people before him and failed.