Freedom of Movement is the opposite of enslavement.
Freedom of Movement allows European businesses to grow faster than Nationalism. The discredited idea that countries should aggressively compete with each other or go to war when trade becomes uneven is the basis of the position that FOM makes things more unfair. The EU is not even a federal body like the USA but it is more modern. Countries that help each other requires that the skills go to where demand is. Immigration of skills from all over the world is the May doctrine. But that impoverishes growth in other countries unless there is a freedom for people to return to their homes and families. Immigration based on skills is permanent relocation of the family rather than a fluidity that causes all countries in the block to grow or benefit from the tourist industry which is also good for growth and citizen awareness.
Being tied to your place of birth means that governments can gouge taxes. It is the trick of the real elites to convince the population of a them and us equation. It is old elitest thinking and is manupulation of the freedoms and rights of people.
Brexit is one example of the inversion of freedom, claiming that “the elites” need to be countered by localisation. The modern world has transport links. Like the fluids moving in the body, freedom of movement flushes out problems, with a sort of international immune system. Nationalism is more like cancer. It results in zones of poverty that can never be resolved.