A peaceful and united world without borders would be awesome. I wish I could be as optimistic as you, but when we have so many examples of one culture completely wiping out another I can’t get there. Tibet is a “recent” example, all Native cultures in North and South America are more. Most of Africa as well.

I do think that not all cultures are equal because all cultural institutions are not equal. Child marriage, caste, women’s rights, LGBT rights, etc. are components that make up cultures, and everyone thinks their culture’s interpretation of these is superior and should be enforced as the norm. This will be THE blocker for a united one world society without borders.

Looking into why there are too many people coming from country X to fix those problems, no matter how generously you are trying to make sure their plate has enough, will invariably run into cultural clashes with fixes. International solidarity and support should increase, but at what point is that cultural colonialism? Can for example Sharia Law coexist perfectly with liberalism? Can a society made with conflicting ideas about autonomy exist?