The paper argues that the different degrees of responsiveness to cosmopolitan concerns can be explained by the relative openness of each institutional layer to public scrutiny and accountability. We employ a theory of justification holding that the political-institutions’ policy-output reflects not only the preferences of their respective decision-makers (internal accountability) but is also sensitive to arguments voiced in the broader public discourse (external accountability). The degree to which external accountability is realized depends on the openness of the respective layers of governance, the existence of a clearly identifiable locus of political responsibility and its exposition to public scrutiny. By tracing the discursive practices on various institutional layers of the European MLG-system, we detail when, where and how institutions respond to cosmopolitan arguments. Our empirical analysis will contribute to a better understanding of the paradox of an EU that is cosmopolitan in ambition but only too often protectionist in practice.