Response to the claim "More black men are in prison today than were enslaved in 1850"

The demography of the US prison population is an atrocity, and there are many statistics that illustrate the fact. But, I've always found this one problematic and misleading because it compares the absolute number, without adjusting for total population growth. (http://www.npg.org/Assets/Images/usprojgrowth.jpg)

Also, from the Bureau of Justice Statistics and The 1860 Census results : In 2009 there were about 2,100,000 inmates incarcerated, 840,000 of which were black (non-hispanic) men. On the other hand in 1850 the slave population was about 4,000,000. Now, if we include probation and parole, in 2009 there were around 7.25 million Americans under "correctional supervision"(probation, parole, jail, & prison). I imagine this is closer to 8 million by now. Given that black men make up roughly half of the incarcerated population, I imagine there are somewhere around 4 million black men under "correctional supervision." That must be where the above stat comes from? (If we recognize that they don't really mean "prison".)

The statement suggests that we are more unjust than we were during slavery. I think the key problem there is "more unjust." We ought to strive to view the our present reality through an objective, historically well informed, and fact-based lens. We certainly have many short-comings as a society, and the demographics of our prison population is foremost among them. But, in an age when opinion, hearsay, and fallacious presentation of statistics are paraded as fact, particularly by the political right, I think we on the left are tempted, and should resist, falling into the same pattern of misrepresenting facts.

The reason I find myself so outspoken about the above claim is that, 1) I have heard it floating around in several contexts over the last few months, 2) from what I can tell it is objectively false, which only serves to weaken the argument for prison reform, and 3) I think it demonstrated a inaccurate reading of our history. We ought to be able to advocate for the eradication of present racism, without denigrating the progress that has been made. I find this especially personal having spent years in Southern Africa seeing first hand race relationships in contemporary South Africa. That experience by no means make me an expert on the subject and I am able to speak from a place of white-privilege, but in my opinion the above claim/meme does not accurately present our current place in history.