I wonder how many of you are familiar with the website Stormfront. They call themselves a "White Nationalist" movement, which is another word for segregationalists, and believe the world would be better if everyone lived with their own "kind."
Their members are fond of saying things like "France for the French, Japan for the Japanese," and draw the logical (sic) conclusion of "The US for whites" from it. They advocate splitting the US into 3 parts, one for blacks, one for whites, and one for Native Americans, and everyone else can "go back where they came from."
The first gaping hole in their logic is that if France is for ethnically French people. then America is for ethnically American people. No, not the sons and daughters of immigrants with American citizenship, but Native American people. Also their "nationalist" philosophy doesn't hold water when you realize that the "white" part of America would allow white European immigration.
Secondly, as you might have noticed, there is no room for mixed-race people in this paradigm. Oh wait, but there is - they take the "one drop" rule even further by saying that mixed-race people would fall into the category of what they consider to be the 'inferior' race - a totally arbitrary hierarchy with whites at the top, and the bottom rung shared by blacks and Jews (who somehow manage to "rule the world" despite their status as the ultimate inferiors). In other words, a person with 1/16 black ancestry would fall into the black category, even if the rest of his heritage was white. I'm not sure how they'd classify a Iraqi-Puerto Rican mixed heritage person, since their hierarchy seems to be only composed of whites, blacks, Asians, and Jews, from what they talk about most.
Going back to their "French for the French" catch phrase, I can only logically assume that white non-French would be booted out as well. Algerians go back to Algeria, so Russians would have to go back to Russia too, right? And I assume they'd treat mixed-ethnic people the same way they treat mixed-race people (especially because in their minds, "Jew" and "Mexican" are races) and base it on GDP or standard of living or something. So if you're 31/32 German and 1/32 Croatian, sorry buddy, you better get out of Berlin.
White Separatists make no attempt to hide their rabid hatred of Jews, and under their "France for the French" policy, Palestine would be given to ethnic Palestinians. So where would the Jews go? Oh that's right, nowhere, this is their ideal world so all Jews would be dead.
The sheer lack of logic in White Nationalist views absolutely galls me, almost as much as the blatant racism does. By seeing the world in black and white, they ignore that many of them are of mixed-European heritage. I'd like to send a mixed Irish-English white nationalist back 400 years in time and have him explain to "his people" how it doesn't matter because they're both white. Maybe then he'd change his viewpoint on how "mixing races" is "tainting the genepool."

Salon.com
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The late, Dr. William Pierce, who in many ways defined America white nationalism, attempted to reconcile the seemingly contradictory ideas with a metaphor about a dog being weakened and eventually killed by blood-sucking fleas. The fleas might have dominated the dog, but that does not mean that they are superior in make-up. I think, though, that it becomes very difficult for most in that "movement" to not begin viewing themselves as inferior.
Afterall, the biggest enemy of white nationalists is not really Jews, like mos tof them say... There's actually a lot more hatred for other white people, whom they believe are traitors to their own race. Since white nationalists have become increasingly maligned in society, they've become increasingly disillusioned and many end up in a sort of self-hating apathy, believing that a race as cowardly as the white race deserves the extinction it is seemingly bringing upon itself.
As for the issue of mixed cultures, I think you make a very good point there, as well. It is silly. Though most white nationalists are not particularly intellectual (and I don't think you'll find the intellectual ones on Stormfront), they have a distorted view of Indo-European. There are actually a minority, who take a somewhat different approach with it, and I think there's a kind of trickle down effect. This is where I suspect, a sort of endearment for Iranians, for example, comes from. Of course some of that is the old "enemy of my enemy" line of thought.
It should be pointed out that nationalism is not strictly a white phenomenon... There's religious bigots and racists of all backgrounds. The white nationalists just seem to get the most attention for some reason.
It's also a matter of some debate amongst them whether or not Italians should be considered white. Then there's some who think poles are not fully white... And more confusingly, there is neo-nazi polish skinheads who seem to hate Germans.... It definitely not a coherent and consistent group. But when you're talking about nationalism you do have to generalize, and the end game for most does indeed seem to be a world of solely white people.
I'm not saying that the separatism is just a front for eventual genocide with all of them. Their are legitimate separatist groups of varying races, and there is some level of coordination between them. Particularity National of Islam and white nationalist groups.
But the majority of white nationalists believe that the "inferior races" are being propped up by the white race, and estimate their eventually extinction if they are left to their own devices.
Not all separatists are necessarily racist, however. There are some people who genuinely believe that the preservation of cultural identity is a positive thing and that miscegenation will eventually lead to a the destruction of cultures. It's an argument one might have difficulty countering, as with time it does seem likely that individual cultures will be swallowed up through intermarriage. It's own of the ironic things about diversity... In order to have any diversity, you need distinct cultural groups...
Personally, I think time is better spent focused on the individual and not getting sucked into the trap of generalization that racialism or racism require one makes. Though culture is obviously part of one's identity, the defining characteristics of a person are based on the spirit, I believe, and that spirit is not confined to considerations of race.
I enjoyed your post! Sorry for the lengthy comments.