It is actually cruel to demand that distinctly different people are all the same and that they must all get along together in the same location

Can't we all get along? The answer is, no, distinctly different people do not get along well together, which is why separate nations and states developed. The one place we are the same is in sharing the same kin-centeredness and ethnocentrism, among the other traditional traits, like localism and gender-differences.

So why then have religious leaders, middlemen, and managers since the dawn of human history tried to make us all get along no matter how different we are from one another? The cynical truth is that the middlemen gain power, at least short-term, from the attempt, even though it has been mainly universalist-globalist-Marxist--pseudo-liberal-neoconservative flim-flam.

It is actually cruel to demand that distinctly different people are all the same and that they must all get along together in the same location, and then when they naturally don't get along to use force to try to create order---but only for a short time.

"Behavioral norms" do not mainly derive from ideology and are not religiously/politically pulled out of the abstract air. Our social behavior mainly comes from the biological origin of our social behavior, which is deeply kin-centered and ethnocentric, among the other traditional traits. 

We can best solve our differences and create order the way we have always done, by forming separate nations and states, which work best as smaller ethnostates. That's the natural way---though not perfect---for us to all get along, while creating distinct cultures that are harmonious with what we actually are.

So who is stopping this? Look to who benefits most from globalism and open borders, no matter how much suffering it causes the rest of us.