What about when the socioeconomic game is rigged against you and has been for most of the last 400 years of American history?
I mean, yeah, poverty is without question a factor--but stopping there feels disingenuous to me. Why are they poor? is then a relevant question, and I think that "because of the racism of old white men" is not the worst explanation I've heard.
OK, but then that's a different issue. It isn't racism in the criminal justice system, and it isn't the criminal justice system's failure. It's the failure of the rest of society.
And even if it is racism originally, it's plausible that it's "because of the racism of dead white men." Two centuries ago they kidnapped millions of Africans and brought them here as slaves. Then they were freed without anyone offering to return them to their original communities in Africa or providing them any resources here to raise successful children. The legacy of that is not going away any time soon even if racism today were totally eradicated, because even in a society with greater upward mobility than we have now, poor parents will always be more likely to have poor children than rich parents.
The root problem is the xenophobia of old white men.
http://www.prisonpolicy.org/graphs/raceinc.html