Random thought about the disdain for SF in literary circles, about what it stems from. Far as I can tell, most of it comes from a few different things, most of which go unacknowledged by literary types:
They're scientifically illiterate, or feel inferior when discussing such subjects (and yet never bother to take steps to correct that deficiency, because it gives them a convenient way to manifest indignity), so SF for them feels like having their noses rubbed in their ignorance.
A variant of the above: they are outright contemptuous of science; some on both the Left and the Right have different incarnations of this, each motivated by their individual ideological prejudices.
They simply aren't aware of SF's genuine literary heritage, or they choose to ignore it.
They resent the populist success of SF as compared to their own niche.
Of the four, I think #1 and #2 are the most unsung, and the latter two are the most self-evident. It's easy to assume that people hate on SF because it's "popular" or "lowbrow", and it's not entirely wrong to start from that assumption. Most negative opinions of SF, even to this day, are rooted it in it being written as crowd-pleasing work, or as material aimed at juveniles -- even when the SF in question just begins from those points and doesn't necessarily end with them.