Political ideologies aside, the ownership of another human is unconscionable, yet has been with our species for thousands of years, with the abolition of such practices only constituting a narrow range of recent years. I don't expect that history can be swept aside so quickly, but that slavers simply move to new methods of control. During the post-abolition years, free men were still excluded from opportunity and full realization of their natural rights, but government itself infringes upon natural rights significantly more than individuals ever have.
There is a good essay on the abolition of slavery by Lysander Spooner (A Plan for the Abolition of Slavery), in which Spooner promotes the ideas of self-ownership and property rights (in which a person can not be considered property of another). The history of slavery was undoubtedly a black mark on society, rightly so, but it's promotion through the state is a reminder that evil men will always use the force of the state to promote their will against that of the common man. Some believe that by enacting laws we can realize a just and fruitful society, but slavery existed in America despite it's conflict with the laws of this nation. The black Jamaican culture has historically been victimized through law by Anglos using the state to continue oppression against them post-abolition, but aspects of slavery persist.
A decade before his essay on abolition, Spooner went into great detail on the Unconstitutionality of Slavery. As a specialist in the field of contract law, he was able to refute many ideas and practices that were in direct conflict with the law, yet practices such as slavery persisted. In The Law, by Frederic Bastiat, the author describes the state's monopoly on the use of force as legal plunder, and applying it to slavery; "in order to make plunder appear just and sacred to many consciences, it is only necessary for the law to decree and sanction it. Slavery, restrictions, and monopoly find defenders not only among those who profit from them but also among those who suffer from them."
There is a paradoxical belief that the state can promote peace and equality through force. Enabling violence to prevent violence is not a path to promote social equality and liberty. Slavery may have been abolished in it's traditional sense, but aspects of it continue today. As Spooner said, "A man is no less a slave because he is allowed to choose a new master once in a term of years." Often, those we see garner support from minorities to promote minority causes tend to use the same system of plunder to either defend or aggress through the state, and many of the policies they support tend to have negative consequences for those minorities they are supposed to be defending.