Stieg Larsson, the Swedish author of the international best-selling “Millennium” series, died in 2004 at age 50 of a heart attack, before the publication of his crime thrillers made him one of the most famous writers of the decade. They have sold tens of millions of copies worldwide, spawned three Swedish films and now Hollywood’s “The Girl with the Dragon Tattoo.”But amid all this, a crucial element often has been overlooked: just how much Larsson embedded in his novels a fundamental passion of his life — his crusade against neo-Nazism and violent far-right movements, which he viewed as anathema to Sweden and to all modern society.