Anyway, it seems to me that librarians must deal with this sort of thing all the time. And the many public libraries that use the Dewey Decimal system can't just fall back on the Library of Congress. Although perhaps there's some central authority that recommends Dewey classifications. But in any case, someone has to decide whether Velikovsky is science or science fiction. Who does? and how?
Quite often, this will be done by the publisher (certainly in my experience with school libraries), who will put a Dewey number on the copyrights page. Not exactly neutral, but that's the way it seems to be done as far as I can tell.
Sam