From Guillaume Faye, Why We Fight:
Philia. Aristotelian concept signifying ‘friendship’ — ethno-cultural consensus between members of the same City.
For Aristotle, democracy is possible only within homogeneous ethnic groups, while despots have always reigned over highly fragmented societies. A multi-ethnic society is thus necessarily anti-democratic and chaotic, for it lacks philia, this profound, flesh-and-blood fraternity of citizens. Tyrants and despots divide and rule, they want the City divided by ethnic rivalries.
The indispensable condition for ensuring a people’s sovereignty accordingly resides in its unity. Ethnic chaos prevents all philia from developing. A citizenry is formed on the basis of proximity — or it is not formed at all. The abstract, integrationist doctrines of the French Revolution envisage man as simply a ‘man’, a resident, a consumer.
Civic spirit, like public safety, social harmony, and solidarity, is based not on education or persuasion alone, but on cultural unanimity — on common values, lifestyles, and innate behaviours.
Societies need something to glue them together; it turns out that having the same basic hardware, and thus the same basic inclinations and abilities, is a necessary but not sufficient condition. This means that without it, you have no glue, but you need other stuff as well to make a society work.
If we flip that around, it means that without ethnic nationalism, no society will survive. Mixed-race societies substitute ideology or dogma for those innate bonds, but these are not as strong, which is why such societies tend to militarize and become totalitarian in order to preserve some unity.
Like so many things, this question brings out the clash between realism and symbolism. In a symbolic sense, you want to accept everyone and be egalitarian, because that way, the individual feels safe from attack. In a realistic sense, you need to select only compatible people and have as few rules as possible.
The Left would design a society around universal acceptance, but it would require a ton of red tape and rules; the Right would design a society around natural selection, and people would have a lot more free time to discover themselves and their world.