By that I don't mean Cosplayers or Manga fans, but rather the "tech" version of nerddom - people who don't follow Manga, Anime, or Idols, but are fascinated with anything if it's related to Japan.
I guess the most obvious reasons are the myth that "nerds" can find sex partners in Japan more easily than in their own culture, and the darker fascination of Western Neo-Nazis (like Breivik) with Japan's alleged racial purity and chauvinistic nationalism. Especially because a mass-murderer has openly stated his deed was "inspired" by Japanese culture, I wonder if the connection has ever been analysed scientifically.