I am going to attempt to give my explanation for why right-wing nationalist ideas exist, how they are comparable to left-wing socialist ideas, and how through this comparison we can see that left-wingers are actually operating on a "higher" level of consciousness than the right-wing.
I am going to start with some seemingly irrelevant (but actually, I think, very interesting) brief information about the history of the development of Marxist thought.
Before he ever cracked into economics, Marx was a philosopher, and a student of Hegel. Many theorists have argued that between the 1840s and the early 1860s, Marx goes through a complete break or change in his thinking, during the time that he began to study economics. There is no doubt that his writings change a lot during this period; he goes from abstract philosophical discussion of (important and interesting) concepts like historical materialism, alienation, the state of man under capital, etc. to a more concrete economic analysis of the capitalist system.
Before the 1860s, Marx mentions to concept of "species-being" several times, and explains that humans are species-beings. A species-being, Marx says, is a species that recognizes itself as an instance of its species, capable of the same thoughts, feelings, and actions as any other member of its species (with some obvious exceptions e.g. some disabled people) and acts accordingly. He goes on to say that this species-being-ness is not always realized in humans; that is, we do not always act in accordance with the fact that we are species-beings: because-and-therefore (dialectics in action) we are not aware of ourselves as being species-beings.
So - how does this tie in to my argument?
The right-wing nationalist cares about people just as much as the left-wing socialist. In fact, what they want (usually unconsciously, except for the NazBols) is a society in which those people that they care about are provided for, healthy and happy, with the scope to realise their ambitions and to preserve that positive experience of life for future generations.
There is nothing un-caring about the views of the right-wing nationalist; when it comes to those people that they view as worthy of caring about - and this is where the concept of "the self" arrives, intimately connected to Marx's concept of species-being.
Now, Marx's concept of species-being can be dismissed as ideological nonsense, of course. But it reflects something quite true; we have a conception of "the self" that goes beyond just "my self". It extends to our children, our bloodline. For most people, it extends to their family, their nieces and nephews, and even beyond that.
I am using the term "the self" here to describe that circle of people deemed worthy of that care. For the nationalist, it is the people of his nation, or at least those that he deems worthy. For the plain old white supremacist, it is all white people (again, at least those that are deemed worthy). For the Islamic fundamentalist, it is all devout Muslims. For the international socialist, it is all humans of the world - the international working class.
The right-wing and the left-wing both operate these circles of care, these wider or narrower concepts of "the self". They both have a sense of "species-being", although only the left has the true species -being. The right settles for "nation-being", or "my-arbitrary-decision-of-where-the-race-barrier-falls-being". So humans are all species-beings, in terms of cognitive operation, really - just with smaller or larger concepts of "self". Only the left-wing is truly realizing their nature as species-beings - the right-wing has not developed their concept of "self" enough yet.
Thoughts? Criticism appreciated, I think this is probably quite wanky and garbled.