Maurizio Ferrera’s essay on how to take EU citizenship forward is an inspiring and welcome contribution to a heated, politicised debate. In my contribution I focus on the tension between the ‘small constituency of mobile citizens’ and those who stay. As researcher we need to engage in fact-finding missions. And there is empirical evidence that mobile EU citizens are net contributors to the public purse. There are still negative externalities of EU free movement that need to be confronted politically. The question then becomes: at what regulatory level and with which means? I suggest that some forms of differentiated integration in this respect may disturb the uniformity of EU rules, but could at the same time increase its domestic support.