Colonel Robert Gould Shaw: It stinks, I suppose.
Trip: Yeah, it stinks bad. And we all covered up in it too. Ain't nobody clean. Be nice to get clean, though.
Slavery can be defined as being forced to work for the benefit of others. It is the antithesis of liberty, where people are free to pursue their own interests.
As such, slavery as practiced in the US, primarily in Southern states, for most of the first century of the country's existence was so glaringly wrong. How could a nation founded on the principle of liberty get it so wrong?
It's simple, really. A fundamental axiom of human behavior is aversion to labor. When presented with an opportunity to obtain economic resources produced by someone else--without commensurate exchange of one's own productive effort, then people are inclined to consider the prospect.
Stated diferently, people are constantly on the lookout for the chance to get something for nothing.
Slavery is one of those get-something-for-nothing propositions. Force someone else to work for you.
In fact, slavery is really a specific category of theft. Theft is the taking of someone else's property against his/her wishes. Property is broadly construed to include life and wherewithal to produce as well as one' personal possessions. As such, murder (expropriation of life), slavery (expropriation of wherewithal to produce), and robbery (expropriation of possessions) all constitute theft.
Textbooks tell us that, in the United States, slavery was abolished with the ratification of 13th Amendment in 1865. Yet, people's axiomatic desire to get-something-for-nothing persists. As such, it is more likely that one form of slavery has been replaced by other institutions with similar characteristics.
One of those institutions is the income tax. In the US, the income tax was institutionalized in 1913 by the 16th Amendment. The income tax gives someone else legal claim to a portion of an individual's productive effort. 'Legal claim' means that this situation is enacted under conditions of force.
Because this condition surely consitutes theft of wherewithal to produce and its economic outcomes, there is no fundamental difference between the taxation of income and blantant slavery as practiced in the Old South.
Currently, about half of all adults in the United States pay income taxes. These people are today's slaves. They are enslaved by those in the other half.