This is something I wrote up earlier that supports the "true diversity" argument;
The solution to multiculturalism- polyculturalism
Polyculturalism- small, 100% homogeneous (religiously, racially, nationally, culturally) nation states with securely defended but "tourist-porous" borders.
Alliances, International institutions, NGO's, trade and free trade agreements, international business and investment, travel and tourism can all work in the same way. Successful nation's economic policies can be copied by others until a sustainable equilibrium is reached of self-sufficiency, sustainability and trade.
Only nationals can own land, rent property for over (say) 6 months and vote in their nation, but as all individuals in the world have their own nation this is fair. I suppose one individual might relenquish their citizenship for another, depending on the involved nations' rules.
Political refugees would ideally be shared out between nations and housed temporarily, repatriating as soon as possible (eg the West could conquer Syria, occupy it, set up a government then give it back to the refugees and normal civilians).
100% homogeneous society ("French", "German" etc) ensures a national consciousness and social cohesion ad infinitum. Societies and economies prosper with a sense of belonging and cohesion like this. There is no opportunity for the seeds of multiculturalism to grow and result in social tension and conflict of interest. However individuals of other nations, races, religions and cultures are welcome to travel, tour and stay for however long the country decides. States work together but are distinct.
Thus global true diversity and unity is achieved, whilst the preservation, participation and fair competition of all different cultures, races, religions, and histories is ensured.
Can we make a list of all the Nationalist movements around the world? Israel is a good example, and anywhere that isn't white, to highlight that it's not racist, it's human nature.
Birds aren't considered racist for roosting with their own kind, and you don't see them warring between each other either.