What has happened is that people, including if not especially sci-fi writers have become enamored with dystopias, and now when shown that it might not have to be that way, they become defensive.
Actually, what happens is that YOUNG sci-fi writers -- especially those born in the 70s and 80s -- approach their art with a bitter cynicism of which the dystopian future is as much a cautionary tale as it is a harsh critique of the present. Strange Days, for example, can be seen as a preemptive indictment of the sort of escapism and petty voyerism inherent in the Youtube generation, while at the same time taking direct pot shots at the moral bankruptcy of the Law and Order paradigm.
Stephenson himself did the same thing in Snow Crash, where the wholesale privatization of just about everything IS the dystopia; there are actually huge tracts of realestate that are perfectly nice to live in, they're just guarded by killer robots and electric fences and anyone who can't get into them winds up living in a self-storage unit. The Diamond Age followed most of the same themes, except it amplified them fifty fold by depicting self-assembling nanomachines that enabled the rich and powerful to custom build entire continents on a whim.
Connect with my above post: where the inheritors of transhumanist technology jealously guard their advantage? In The Diamond Age, the world's most powerful educational tool winds up in the hands of a poor girl only after her big brother clobbers its lead programmer with a nunchaku. That underscores a growing trend in modern fiction in general: it's a lot less about the technology than it is about the PEOPLE.