The pessimism and dystopia in sci-fi doesn't come from a lack of research resources on engineering and science. It mainly comes from literary fashion.
If the fashion with editors is bleak, pessimistic, dystopian stories, then that's what readers will see on the bookshelves and in the magazines, and authors who want to see their work in print will color their stories accordingly. If you want to see more stories with a can-do, optimistic spirit, then you need to start a magazine or publisher with a policy of favoring such manuscripts. If there's an audience for such stories it's bound to be feasible. There a thousand serious sci-fi writers for every published one; most of them dreadful it is true, but there are sure to be a handful who write the good old stuff, and write it reasonably well.
A secondary problem is that misery provides many things that a writer needs in a story. Tolstoy once famously wrote, "Happy families are all alike; every unhappy family is unhappy in its own way." I actually Tolstoy had it backwards; there are many kinds of happy families. Dysfunctions on the other hand tends to fall into a small number of depressingly recognizable patterns. The problem with functional families from an author's standpoint is that they don't automatically provide something that he needs for his stories: conflict. Similarly a dystopian society is a rich source of conflicts, obstacles and color, as the author of Snow Crash must surely realize. Miserable people in a miserable setting are simply easier to write about.
I recently went on a reading jag of sci-fi from the 30s and 40s, and when I happened to watch a screwball comedy movie ("His Girl Friday") from the same era, I had an epiphany: the worlds of the sci-fi story and the 1940s comedy were more like each other than they were like our present world. The role of women and men; the prevalence of religious belief, the kinds of jobs people did, what they did in their spare time, the future of 1940 looked an awful lot like 1940.
When we write about the future, we don't write about a *plausible* future. We write about a future world which is like the present or some familiar historical epoch (e.g. Roman Empire), with conscious additions and deletions. I think a third reason may be our pessimism about our present and cynicism about the past. Which brings us right back to literary fashion.