Are these bands spreading a message of racial separatism, among other things? Absolutely. Are a bunch of xenophobic, twenty-something European metalheads, making demos on the cheap, really that much of a threat? Probably not (though the very spread of these sentiments is always corrosive.) Is the music—some of it anyway—curiously absorbing? Well hell, yes, or I wouldn't even be typing.
The best thing an inquisitive metalhead can do in this situation is to not give your money to these artists. If you want to sample some choice, down 'n' dirty National Socialist Black Metal, there's a very comprehensive blog called Wotan mit Uns that has newer stuff as well as "classics" up for download. There's a year's worth of daily posts to sort through there.
The appeal of a lot of this stuff is that sonically it takes black metal down yet another, wretched, twisted alley, somewhere between lo-fi art damage and punk, conceived in a garage full of guitars, amps, drums and sadly, swastika flags. If these bands took a stance instead for art deco, or against deforestation—and sonically stayed the same—we'd all have no problem with it; the music would just be another weird-ass subgenre, which is really what it is.