3)There is no religious justification at all for excluding other races. The concept is not mentioned, even once, in any Edda or Saga. If it were such an important part of heathenry as Folkists of the first two types make it out to be, then it would have received at least a passing reference by the ancients. It's not like they were unaware of other races. They were great travellers, explorers, traders, conquerors, who ranged far into eastern europe and even into northern africa. So it is quite apparent to anyone not trying to shut their ears against what they don't want to hear that the real motivation of these Folkists is not religious at all, but political. That this is so can be seen by visiting the message boards and websites of such Folkists. Many focus primarily on the issue of race and such political issues, mentioning actual religious ideas little, if at all. One popular message board I visited for White Power Folkists and the second type of Folkist (the honestly intentioned, if confused type) had a total of 72 threads that had little to nothing to do with religion in any way, about a third of which were concerned with issues of race. It had only 25 threads on religious topics. This same board had, as its introduction, a long rant about White Power and the need to exclude other races from Asatru but it literally had nothing at all about the practice of the religion. In contrast I know a black man who honors Thor as a patron, and accepts the ancient heathen culture and religion as guiding principles. When he talks it is about religious matters, not political ones. About Loki's true nature, and why one should or shouldn't walk Odin's path. About the less well known aspects of Thorrish worship. Its not difficult to tell who is the more truly religious.
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The members of the middle faction of modern Asatru are called Tribalists, and shun the errors of either extreme. The racism of Folkish practice is avoided as well as the "anything goes" motto of the Universalists. The answer the Tribalists have to the question of "Who can practice Asatru?" is: "Anyone who makes a sufficient effort to understand and adopt the culture of the ancient heathens." This gives Asatru rigorous enough standards to make sure our practice is like that of the ancients, and is well understood, for to fully adopt another culture requires MUCH study. Additionally the gods first came to be known in the context of the ancient culture, so it stands to reason that they can only be truly understood in the terms of that culture. It also keeps us from the untenable argument that "other races" are somehow so intellectually inferior to the Norse and Germanic that they cannot attain this understanding. After all, someone brought up in modern Western culture is quite likely, from childhood on, to have been inundated with images, stories, and ideas from that Western culture, thus including our religion. This would make anyone in our culture, whatever the color of the skin, likely enough to have a way of thinking predominantly drawn to Asatru in religious matters, and much more ready to understand it, than some religion their ancestors happened to practice so long ago it isn't a part of their lives anymore.
After all, even the Europeans have been living on that land for awhile now and it makes sense that some would want to honor the Gods and Spirits of the land and water in the Native fashion. Like painted wolf pointed out, many Europeans and Africans became adopted members of First Nations tribes. European settlers were known to run away from the white settlements and be absorbed into nearby tribes because their ways were more appealing to them. Sometimes, the other white settlers would kill those who did that. Maybe they were jealous. 
