What kind of border policies would facilitate social cohesion in egalitarian post-migration societies? Are immigrants harming welfare state policies? Why do the major immigrant-receiving societies of the last 50 years still conceive of themselves as ‘culturally homogenous' societies? This dissertation answers these popular, everyday questions by reconnecting ‘frame analysis', normative political philosophy and social sciences in an unprecedented manner. It argues that unless immigrant-receiving societies conceive of themselves as culturally, religiously, racially and ethnically diverse, then this frame will have harmful consequences for egalitarian societies, especially those with a generous Welfare state. This argument is controversial in normative political philosophy, given social cohesion, to the extent that it requires a commonly shared national identity, favors restrictive border policies. Instead, according to the egalitarian necessities of the national states of our time, border policies should be morally much more open than they currently are.