Freedom was impossible until slavery had created the material conditions for it. Indeed, Engels put it in so many words, praising the "progressive" achievements of slavery and successive forms of class exploitation as necessary preconditions of socialism (much as Christian theologians praise the felix culpa, or "happy sin" of Adam, for making possible the beatific state of redeemed humanity).

It was slavery that first made possible the division of labour between agriculture and industry on a larger scale, and thereby also Hellenism, the flowering of the ancient world.. Without slavery, no Greek state, no Greek art and science; without slavery, no Roman Empire. But without the basis laid by Hellenism and the Roman Empire, also no modern Europe. We should never forget that our whole economic, political and intellectual development presupposes a state of things in which slavery was as necessary as it was universally recognized. In this sense we are entitled to say: Without the slavery of antiquity no modern socialism. –Friedrich Engels, Anti-Dühring

...The anarchist position, in contrast, is that exploitation and class rule are not inevitable at any time; they depend upon intervention by the state, which is not at all necessary. Just social and economic relations are compatible with any level of technology; technical progress can be achieved and new technology integrated into production in any society, through free work and voluntary cooperation. Likewise, any technology is amenable to either libertarian or authoritarian applications, depending on the nature of the society into which it is integrated.

–Kevin Carson, Studies in Mutualist Political Economy