The Roman empire was based on slavery and had to die so that humanity could progress. Slave labor is vastly less efficient than having serfs that can keep (part of) what they produce and have incentives to +-work harder. That allowed producing more food with less workforce so many people were free to do other things and bigger cities could develop which in turn would set the foundation for making the industrial revolution possible.
Everything else is just some weird romanticism of the antique when in reality many things got better in the medieval period. There wasn't a sudden fall of the Roman Empire. It was a gradual process and the structures coming after it saw themselves not as a replacement but as a continuation of Roman traditions.
Edit: As people misunderstand. The important difference between serfdom and slavery is not freedom. The important part is incentives to work harder. Slaves only have the incentives to avoid the whip. They do not own what they produce. They need to be closely supervised and micromanaged. In contrast many forms of serfdom allowed to the serfs to keep some of the stuff they produced so they had incentives to work more efficiently.
Everything else is just some weird romanticism of the antique when in reality many things got better in the medieval period. There wasn't a sudden fall of the Roman Empire. It was a gradual process and the structures coming after it saw themselves not as a replacement but as a continuation of Roman traditions.
Edit: As people misunderstand. The important difference between serfdom and slavery is not freedom. The important part is incentives to work harder. Slaves only have the incentives to avoid the whip. They do not own what they produce. They need to be closely supervised and micromanaged. In contrast many forms of serfdom allowed to the serfs to keep some of the stuff they produced so they had incentives to work more efficiently.