The authors are to be commended for letting their subjects speak for themselves, rather than presenting the reader with an editorial on the evils of white supremacist movements and using selected quotations to back it up. That said, I find the book incredibly frightening: the members of the groups profiled have made the common mistake of confusing "We're sincere" and "We can find Biblical support for our beliefs" with "We're RIGHT." (In fact you can find Biblical justification for just about anything, but that's never stopped anyone.) They resent being lumped together with "racist groups" by the FBI et al., but they themselves lump all sorts of unrelated phenomena together and call it the Satanic plot to take over the world.
These groups may contend that they're not "racist," but according to the maxim attributed to the late Cardinal Cushing: if it walks like a duck, and swims like a duck, and quacks like a duck, I say it's a duck.