I don't think it was a bad idea to stand up and say "fuck you" to NSBMers, I wouldn't want my music to be used for any political agendas either. The fact that Summoning aren't necessarily an NSBM band puzzles me as to why anyone would use their music for a nazi video. I don't think he went about it very well though, he said a lot of poorly informed things that, frankly, I was surprised to hear from somebody in a black metal band of their caliber. For example, since when was Stalin a fascist?
I don't know what the situation in Europe is, but most people that show up to concerts around here that listen to NSBM aren't true nationalists. They're racists, and hillbillies to boot. So for that I have something of a prejudice against it, I think they're a squee-bit naive in some of their beliefs. A little bit oversimplified to ever work. "If only we could just get them damn african-americans to quit terkin' our jerbs", and similar rhetoric.
I'm not defending multiculturalism, but I am suggesting that unless the music is good, NSBM shouldn't be supported as a whole. Nationalism's cool, and so is taking pride in your heritage, but when your music revolves more around ignorant, sophomoric, and naive prejudice than it does metal, you suck.