Who's Afraid of the Future?

This summer I read the novel Oryx and Crake by Margaret Atwood. It's an excellent read - my friend Garry has even put it on his exclusive Top 5 Books list. It's a cautionary tale set in the relatively near future, where genetic engineering has changed the world in many ways. One feature of this world is that there are extreme class divisions in society. The point of this post is to ask why most stories that are set in the future tend to portray the upcoming years very darkly with respect to class differences, when the overall trend of western society over the past few hundred years has been the erosion of class differences. I would argue that you're not only much better off being poor now than you were 200 years ago, you also have a greater potential for socioeconomic mobility now than you did then. Some people would point out that this has been changing recently (this is of course debatable), with the upper class is holding more power, but it is interesting to see how so many futurisitic stories paint a vision of society where an elite class holds itself far apart from the commoners. Others also point out that with the popularity of gated communities, etc., that many of the features of Atwood's novel are already with us. But in the long run, I see our society as becoming less class-based as history progresses. So the question becomes, more broadly: when most people would agree that human existence has generally improved over time, why do our stories posit a future where this trend ceases to hold true in many ways? Is it merely a function of a pessimistic view of the future (or nostalgia for the past) that is extremely common in our society, and if so, why do we have such a negative outlook when the evidence should have us feeling the exact opposite?