Author Robert Heinlein took great pride in his military service, having graduated from Annapolis and served in the Navy. In a letter to fandom leader Forrest J. Ackerman, Heinlein condemns science fiction fans who didn't participate in WWII efforts.
Heinlein wrote this letter to Ackerman — Ackerman being a science fiction editor and early promoter of scifi fandom — after the death of Ackerman's brother at the end of World War II. It's an interested letter not only because Heinlein disparages fans who didn't participate in the war effort — be it as soldiers or civilians — but also because he felt science fiction wasn't reaching its potential as a social tool. Heinlein condemns what he sees has an overindulgence in escapism at a time when humanity needs literature that combats hatred and advocates for civil liberties.