For those who came in late, the Mundanes hold:
Now while I applaud the Mundaners their laudable concern for our own little blue marble, I believe that it is way-dangerous to make predictions that close the book on hitherto undiscovered technologies. This seems naive even without having to invoke the famous Charles Duell patent office legend. Nor, last I checked, has the jury yet come in on the multiverse. (See, for instance, physicist & science writer Michio Kaku's recent work, Parallel Worlds.)
That interstellar travel remains unlikely. Warp drives, worm holes, and other forms of faster-than-light magic are wish fulfillment fantasies rather than serious speculation about a possible future.
That magic interstellar travel can lead to an illusion of a universe abundant with worlds as hospitable to life as this Earth. This is also unlikely.
That this dream of abundance can encourage a wasteful attitude to the abundance that is here on Earth.
That there is no evidence whatsoever of intelligences elsewhere in the universe.
That absence of evidence is not evidence of absence -- however, it is unlikely that alien intelligences will overcome the physical constraints on interstellar travel any better than we can.
That interstellar trade (and colonization, war, federations, etc.) is therefore highly unlikely.
That communication with alien intelligences over such vast distances will be vexed by: the enormous time lag in exchange of messages and the likelihood of enormous and probably currently unimaginable differences between us and aliens.
That there is no evidence whatsoever that quantum uncertainty has any effect at the macro level and that therefore it is highly unlikely that there are whole alternative universes to be visited.
That therefore our most likely future is on this planet and within this solar system. It is highly unlikely that intelligent life survives elsewhere in this solar system. Any contact with aliens is likely to be tenuous, and unprofitable.
That the most likely future is one in which we only have ourselves and this planet.
Leaving aside these quibbles, they are partially correct in their criticisms of past and contemporary "Wide Screen Space Opera," as Ian concedes when he writes, "Whatever kind of humanity makes it into interstellar space is not going to be like us. It’s needs and ecological niche will be very different."
Claiming that we can't make it into space ever, at all, in any way, shape or form, however, is very different from asserting that we can not make it as we are now. The Mundanders seem, then, to be arguing a focus on near-future extrapolation vs. far future vision.
But Ian further comments, "If we confine ourselves only to the most likely near-future, does MSF run the risk of becoming almost a shared-world anthology, a future history?"
In the introduction to my 2003 anthology, Live Without a Net, entitled "Disengaging from the Matrix" I argued against what I perceived at the time as an apparent bottleneck in our speculative futures. I wrote then that, "one has only to read Wired magazine and Scientific American with any regularity to see that some form of that Gibsonian existence is barreling down upon us with ever-increasing speed. As advances in computerization, miniaturization, and neural interfacing are being made every day, it becomes increasingly hard for writers of speculative fiction to imagine near-future scenarios that do not contain at least some of the tropes of cyberfiction. "
Now, the anthology was a long time in the making, and I was really writing from a cusp-of-the- millennium perspective, talking largely about an American-only SF scene that seemed obsessed with VR simulations and post-cyberpunk and which had yet to embrace the New Space Opera, the full importance of the Vingian Singularity, the New Weird, et al. to the degree that swiftly followed. But I still hold that a restriction of imagination for whatever reason - whether internally imposed or externally compelled - is an undesirable thing.
Charles Stross makes the very good point in his comment wherein he says that "declaring that certain technologies are almost certainly not going to happen therefore we shouldn't consider the consequences of them is almost certainly about as wrong-headed as you can get..."
I think that the problem stems in part from the fact that science fiction has evolved to fulfill multiple roles, and each successive movement or manifesto that comes along seems to section off one of them in isolation from or opposition to the rest.
If I may...
Science fiction can serve as an actual communicator of science and the scientific worldview. As such, it may employ the rigorous application of current scientific principals, but it need not do so in order to communicate a general sense of the value of a rational (verses a superstitious) world view. (I would suggest that this is an increasingly-important function in America's current political climate. Intelligent Design anyone?)
Science fiction can serve as allegory, as social criticism, as a lens for examining the present by casting it in the future. As such it can employ loose or rigorous extrapolation, though it is not by any means obligated to do so and its extrapolation may be exaggerated for satirical effect. (Again, see parenthetical above as to the current importance of this aspect of SF.)
Science fiction can serve as predictor, as prognosticator of the future. As such it generally strives for rigorous scientific extrapolation, and as such, it is generally wrong. That it is often wrong is not the point. (And it is sometimes right!) But in that it serves as a community of forward-looking individuals in part dedicated to the idea that technology creates social change and to the examination of the ramifications of each new technological potentiality in advance of its actual development and implementation is value in and of itself. (A value which, one wishes, was paid more attention in light of the absurdity of certain Congressional debates on stem cell research and cloning. The work has already been done for you folks. If you only paid attention...)
Science fiction can serve as catalyst for the future. The number of SFnal devices that were later created by enthusiastic engineers and inventors is too numerous to list here, though examples range from Clarke's communication satellites to Captain Kirk's cellphone to Geordi LeForge's visor. The website Technovelgy is a good start for some contemporary examples. (In this regard, it seems clear that even bad science fiction can serve as the catalyst for invention.)
Finally, yes folks, science fiction can serve as entertainment. And that may be my most strenuous objection with the Mundaners. They seem to have forgotten that it's okay to have fun. (And in an age where science fiction literature is loosing rapid ground to its less-informed cinematic counterpart, sacrificing SF's entertainment value may be cutting off one's nose to spite one's face. It is certainly counter-productive to communicating one's message.)
I think I'm fine with any movement that seeks to describe one aspect of science fiction however they want, but I'm opposed to any movement that seeks to proscribe for the rest of us. And in closing, I want to summarize with a quote by Arthur C. Clarke who wrote, years ago, that "the limits of the possible can only be defined by going beyond them into the impossible." Like Lewis Carroll's Alice, I think we should all strive to believe three impossible things before breakfast. Maybe by lunch, one of them won't look so improbable after all. And by dinner time, it might even be a reality. And if not, we were still guaranteed an interesting day.