Slavery is forced labor, regardless of whether or not compensation is given. Libertarianism is the philosophy of liberty; notice the root word “libert”arian. Liberty is the whole point. Obviously, by definition, slavery would be outlawed in a libertarian society because slavery uses aggressive force (or the threat there of) and violates the freedom of the individual. Historically, governments have usually sanctioned and enforced the tyranny of slavery. In a libertarian society, not only would it be impossible by definition for a government to enforce the institution of slavery, but the government would also be obligated to actively end slavery and prosecute slave holders since a legitimate role for the government is to stop people from violating other people’s freedom rights. All humans would have the same fundamental natural rights, enforced by law.