The genocides are, why a country splitting to release a ethnic group, is something to celebrate. Less chance of that to happen. Pakistan/India seperation comes to mind. Its better to seperate halfway peacefully, then stay together and then get the great murdering during some more despotic moments in history. Can still form something like the european union, to not be bullied by the great bullies.

Its of course, orthogonal to multi culturalism as a ideology, but all the melting pots without a constant economic flame, imploded into civil war (libannon, jugoslavia) or turned into brutal centralist empires (russia, etc.).