DanBC - You are drawing conclusions from insufficient data. You assume that black prisoners serving time for drug convictions are disproportionately punished.
In reality, as widely documented, drug busts are often the only way to get a violent person off the streets. It's not "justice" per se, since they're sometimes punished for the lesser crime, but police typically know who the bad guys are in their neighborhood, who the likely murderer or rapist is, who's breaking and entering, but it's not all that easy to apprehend someone and get a conviction. And if they don't get a conviction, there's the risk of double jeopardy -- can't be prosecuted for the same thing twice. So sometimes it's more expedient to get them off the streets on a lesser charge such as possession.
If you explore the U.S. Bureau of Justice Statistics (bjs.gov) you will discover some startling and depressing facts. About half of the roughly 16,000 gun homicides per year are committed by black males 16-39, and most of their victims are also black. What takes so many black males out of society can be explained by this type of statistic -- gang bangers fighting it out in the ghettos. (Hispanics are also disproportionately represented, but not as highly as blacks.) By contrast, the majority of white deaths from guns are suicides.
Indeed if it weren't for this tragically high violence among Blacks, guns would hardly be considered a political hot potato issue in the U.S. because per capita violence would be about on par with Canada and Western Europe.
Then of course there are many other crimes of violence and property -- robberies, muggings, rapes, B&E, shoplifting, etc., that snare black youth in the legal system for years.
The U.S. has a socio-economic problem with the African-American population that has not alleviated, 50 years after the Civil Rights Act that emancipated Black people, gave them the power of the vote, moved the country toward greater protection of minority rights, and opened the legislative door to quotas and affirmative action to try to uplift the black population economically.
Obviously, there is still racism in modern day U.S. society, but it is almost more notable by its infrequence, e.g. the headlines that happen every time a white cop shoots a black suspect, a tiny fraction of overall shootings yet given disproportionate attention by society because of residual outrage at the casual profiling and brutality from an earlier era.
What can be done? In my opinion, economic development would help to alleviate these problems more than almost any other solution that's been tried. I would focus on ghetto areas, both black and Hispanic, and designate them as "special economic zones" that would have greatly reduced taxation and regulation, similar to what's been successfully done in China and other developing areas. For example, an entrepreneur would be able to establish a factory in an SEZ with minimal EPA scrutiny and minimal paperwork, something that normally would take months or years, with all sorts of NIMBY lawsuits and red tape.
Get people working real jobs, get them on a path to middle class prosperity, and their children will see a way out of the hopelessness and despair that characterize the ghettos.