The elimination of trade barriers and promotion of the free exchange of capital are big positives in the creation of a common market. However, the people in charge will never resist the urge to buy constituencies and level the inequalities within the system by shifting resources from the "haves" to the "have nots." That is when the free market principles that led the creation of the common market go out the window. That is what happened in the USA (The issue was settled in favor of union in our civil war) and that is what is happening in Europe. Unfortunately, the EU has no standing army to enforce it prerogatives.
Disintegration is therefore inevitable.