I don't have the time to do the research justice at this moment; however, let me lay out a rough argument.
Let us say, for the sake of argument, that poverty and drug abuse are strongly correlated. Poverty does not cause drug abuse, but people in poverty are more likely to abuse drugs, and people who abuse drugs are more likely to be in poverty due to their drug abuse. The article seems to agree with this point, as it points to working class people as the focal point of abuse of cocaine. In 1900, the white population was approximately 60 million and the black population was approximately 9 million. Casual research suggests that 50% of children were in poverty, which I will extend to suggest that 50% to families were in poverty. Let us; however, assume that only 30% of whites and 100% of blacks were in poverty. In this case, black working-class people were still a minority of working-class people, at a ratio of 2:1.
Under this assumption, is it reasonable to assume that cocaine abuse in non-white communities was the sole catalyst for this change?