Margaret Atwood vs. Carl Sagan
I haven't actually read Margaret Atwoods In Other Worlds, but I understand from articles and reviews that she takes the position that "if it is realistic or plausible, it isn't science fiction". Well, even if one accepted her pronouncements that aliens and spaceships weren't either of those, there's still plenty of stuff written by science fiction writers, some of them recognized Grand Masters such as Heinlein and Asimov, that was quite realistic and plausible. Beyond that, well, spaceships exist and further development of them is in no way implausible (although FTL may well be), and as to aliens? Ms. Atwood, I'm afraid I'll take Dr. Carl Sagan's opinion as to whether the existence of aliens is plausible or not over yours.
In short, Ms. Atwood seems to have confused her definitions of science fiction and fantasy, although I'll happily concede that much of what people call science fiction is actually science fantasy or space adventure.