-"Fiction always reflects the time in which it's written, not the time in which it's set. So what's the problem?"-
The same is true of Shakespearean criticism. But that's not what it's supposed to be about; it's supposed to be about Shakespeare in his own time and place. And it's true of historical nonfiction, academic or popular.
And: some people, including me, read fiction set in the future hoping to find something new. To us, "just like today" is no more satisfying than "They realize neither of them is interested in sex and both prefer to live alone" would be to most romance readers.
Not to mention that things might change before a story is published. For several months after the Soviet Union fell, "Soviets invade America" novels were still turning up in bookstores. There were probably others in the pipeline or being written which no one will get to read.
It's not possible to predict the future with total accuracy. But there are ways to cut down on bloopers.
1) If you graduated from high school thirty years ago, don't take for granted that nothing has changed. Check.
If you graduated last year, it still might be a good idea to check.
Yes, teenagers will still act like teenagers. But they won't wear the same clothing, listen to the same music, use the same slang. And for how long has it been possible for a lesbian couple to be elected Homecoming King and Queen? (See the March 2012 issue of Seventeen.)
Places you haven't been to in a while have undergone change. In 1965, some Paris restaurants had hectographed menus in their windows; this is probably no longer the case. (This wasn't mentioned in any guidebook I read. If you visit any place, and don't notice anything which isn't in guidebooks, I recommend an immediate medical checkup.)
2) Look at what's already happened which will have highly-predictable consequences.
When "Jennifer" became the most popular girl-baby name in the US, it was easy to predict that in a bit less than twenty years there would be a lot of college women named Jennifer.
It should have been obvious that the Baby Boom meant larger college classes down the road. I think most college administrators realized this around 1964, but it might have been later.
3) Certain predictions keep being made, and keep being wrong. "In a few years, everyone will have at least one flying car." "Once this law is passed, the problem will be solved forever." (If you want to write alternate history in which ground cars became obsolete in 1960, and Prohibition resulted in all Americans giving up alcohol, that's another matter.)
4) Check to make sure you know what's really happening now that will affect the future. By the late 1980s, it should have been obvious that the Soviet Union was in no shape to successfully invade the US.
5) Take account of moral panic cycles. Right now, nonconsenting sex is A Big Problem: in US colleges, in science fiction fandom, in religious organizations. Drunken driving is also seen as more of a problem than used to be the case. Such jokes as "If you drink, don't park. Accidents cause people" are no longer as acceptable as they once were.
Tobacco use has become much more restrictive. And there are no longer ads like "Reach for a Lucky instead of a sweet."
Conversely, marijuana has become acceptable enough to be legal in several US states; and various other countries (Portugal, for example) have decriminalized it.
And there are reciprocal cycles. In certain times, even clueless hard drug users realize that heroin is Bad News. Many turn to nice, safe cocaine. Later, such people realize that cocaine is Bad News and turn to nice, safe heroin. (Any resemblance to political cycles is left to your imagination.)
6) Eating habits will change. Once, most Americans had never tasted pizza. Pasties weren't always a Finnish-American dish in the Upper Midwest.
