Diversity and pluralism are embedded in the political project of the Union as based on the archetype of a liberal “open society”. At the same time, the preservation and promotion of these values is being increasingly challenged, especially in the fields of EU competence which are traditionally more sensitive to the calls for sovereignty, such as on migration and asylum policies. This article takes the EU immigrant integration policy as a case study to test the legal boundaries of the European open society. It departs from the limits of the EU competence in this field of action to demonstrate that the self-restraint of the European Union in the development of “a more vigorous integration policy” has been first and foremost a political option. This option has magnified the tension embedded in the legal design of the AFSJ and the CEAS, minimising the correlation between successful integration paths and effective immigration and asylum policies. This evidence should induce the Union – within the remit of its own competence – to greater activism in support of TCN integration and inclusion in the European open society.