Why do you think that Mother’s Younger Brother chose to help Coalhouse Walker, Jr.?

Mother Younger's brother is trying to find himself (and might I say he looks in all of the wrong places); he's depressed and feels himself spurned by Evelyn. When he decides to help (follow, join) Coalhouse's group, he does so to gain a sense of purpose, a sense of belonging, and for whatever misplaced reasoning this group of revolutionaries gives him what he's looking for.

"They believed they were going to die in a spectacular manner. This belief produced in them a dramatic, exalted self-awareness. Younger Brother was totally integrated in their community. He was one of them. He awoke every day into a state of solemn joy."