Why have we stopped being optimistic about the future?

Virginia Postrel writes:

I sympathize with science-fiction writer Neal Stephenson and venture-capitalist Peter Thiel, whose new books lament the demise of grand 20th-century dreams and the optimistic culture they expressed. “I worry that our inability to match the achievements of the 1960s space program might be symptomatic of a general failure of our society to get big things done,” writes Stephenson in the preface to "Hieroglyph," a science-fiction anthology hoping “to rekindle grand technological ambitions through the power of storytelling.” ...

[W]e have plenty of big projects. The human genome has been sequenced. Enormous libraries of books and collections of paintings and drawings have been scanned and made searchable online. James Turrell is making great monumental art in the Arizona desert. Three -- three! -- billionaires are running their own space programs. Space is so popular among his peers that Bill Gates, whose own modest goals run to conquering malaria and other tropical scourges, finds himself telling interviewers that “it’s not an area that I’ll be putting money into.” If there’s public malaise about progress, it isn’t because nobody is doing anything bold....

The reason mid-20th-century Americans were optimistic about the future wasn’t that science-fiction writers told cool stories about space travel. Science-fiction glamour in fact worked on only a small slice of the public.... People believed the future would be better than the present because they believed the present was better than the past. They constantly heard stories -- not speculative, futuristic stories but news stories, fashion stories, real-estate stories, medical stories -- that reinforced this belief. They remembered epidemics and rejoiced in vaccines and wonder drugs. They looked back on crowded urban walk-ups and appreciated neat suburban homes. They recalled ironing on sweaty summer days and celebrated air conditioning and wash-and-wear fabrics. They marveled at tiny transistor radios and dreamed of going on airplane trips.

Then the stories changed. For good reasons and bad, more and more Americans stopped believing in what they had once viewed as progress. Plastics became a punch line, convenience foods ridiculous, nature the standard [warning: New York Times link] of all things right and good. Freeways destroyed neighborhoods. Urban renewal replaced them with forbidding Brutalist plazas. New subdivisions represented a threat to the landscape rather than the promise of the good life. Too-fast airplanes produced window-rattling sonic booms [NYT link]. Insecticides harmed eagles’ eggs. Exploration meant conquest and brutal exploitation. Little by little, the number of modern offenses grew until we found ourselves in a 21st century where some of the most educated, affluent and culturally influential people in the country are terrified of vaccinating their children. Nothing good, they’ve come to think, comes from disturbing nature.