Just came across this wonderful quote in Better to Have Loved: The Life of Judith Merril. Judy was a friend and mentor of mine, and her posthumous memoir, co-written by my friend Emily Pohl-Weary, is nominated for the Hugo Award this year.
Whereas in other literary fields you wouldn't dare take an idea from another writer and use it, because that would be considered plagiarism, science fiction people loved to build on each other's stories. The business of giving away ideas and promoting other people's work was a part of the community at large.
The Futurians did this to an amazing extent. For example, every Futurian had a pen name that included the family name Conway. A good number of the stories that appeared in science fiction magazines at the time were written by someone-or-other Conway.