And your link makes clear the Barbary form of slavery had little in common with the extreme form practiced in the US.
The violent rejection of England and monarchy allowed the founders to make a dramatic break from the past. A new approach to human rights, a government of the people, for the people. Ideals broadcast and institutionalized via the Declaration of Independence, the Constitution, and the Bill of Rights.
"We hold these truths to be self-evident, that all men are created equal, ..."
All the mindful attention, negotiation and agreements, toward implementing a system explicitly establishing liberty and justice for all, adds a thick layer of criminal responsibility for the systematic exception made, to continue upholding one form of extreme injustice. The complete violation of all those principles, held dear, for one unfortunate group.