The Western hemisphere has witnessed recent increased immigration flows generating social and political debate across Europe. In one view, migration flows represent an opportunity to construct a diverse social cohesion. In another view, migration flows are perceived as a threat to existent national cultures. This view is held by political nationalisms and right-wing populist forces installed in the majority of EU countries' parliaments, accentuating discrimination against immigrants and residents in Europe. We theorize that European identity predicts positive attitudes toward immigrants (prosocial behavior and support for inclusive policies), whereas national identity's predictions of attitudes toward immigrants' inclusion depends on participants' political tendency. Moreover, we test the mediation effect of positive (humanitarian concerns and economic benefit) and negative (jobs scarcity, cultural deterioration, and invasion) arguments used in political discourses regarding immigrants' inclusion on the relation between national and European identities and attitudes toward immigrants' inclusion. Results (Portuguese sample, N = 176) show that national identity predicts negative attitudes toward immigrants' inclusion, but only among right-wing individuals. Among left-wing individuals, national identity predicts less contestation to immigrant's inclusion sustained by humanitarian concerns. Interestingly, European identification weakened right-wing individuals' adherence to discriminatory arguments and increased perceived economic contribution that immigrants bring to society, increasing agreement with prosocial behavior and immigrants' inclusion. We discuss that European identity, sustained in humanitarian values and economic benefit, may stimulate a stronger multicultural social cohesion, intergroup trust, and social wellbeing based on democratic values, social justice, and equality, and on the respect for human dignity.