We love movies about space, but are continually bored by actual space travel. When's the last time you rushed to the TV to watch a space shuttle take off?
No, we all seem to be waiting for the future of space travel to get here, a future of huge, comfortable starships hauling us to other planets where adventure awaits. Hopefully ships with lasers, that can destroy other ships.
Unfortunately, it appears that even for your grandchildren, space travel will really, really suck. Mainly because...
6There is No Sex in Space
If Battlestar Galactica taught us anything, it's that the starships are like the Love Boat, if it were filled with never ending robot orgies and counterproductive human sexual drama. It's perfectly natural for the crew to spend their off hours doing some space romance, or as experts call it: "Boldly going where Kirk has gone before."
Places like the cavern o' dicks.
Let's start with the physical challenges. First of all, being in space lowers your blood pressure and slows down the flow of blood overall. That means you almost certainly can't get a boner. So there's that.
"I'll take that challenge."
If you somehow are able to achieve a zero-G erection, you'd better damned well make sure you've got multiple forms of birth control in effect. Think about it; they're not going to stock an interstellar mission with tens of millions of dollars of extra supplies on the off chance an extra crew member will pop out of somebody's womb. But that's not the only reason a pregnancy in space would be bad news.
Experiments done on mice embryos have shown that a lack of gravity messes with an egg's ability to properly develop. Add to that the markedly higher doses of radiation an astronaut is typically exposed to, and the result is not going to be something whose picture you'd want to keep in your wallet.
Of course, we've avoided the most obvious reason: you don't have to have spent time around too many dating couples at the office to know how it screws up the team dynamic. Take the bickering and innuendo and breakups and crying, and imagine being stuck with that while sealed inside a huge metal tube for several years.
Dead. Both of them.
Even now, NASA doesn't allow married couples to go on the same trip (there has been one exception, where the couple got married right before launch and it was too late to change the plans). As NASA knows, the true power of love is its ability to make even brilliant, highly skilled people turn into kidnap/murder plotting, 500 mile driving, diaper wearing crazy people.
That simply can't happen on a starship--romantic entanglements would have to be forbidden. You'll have to be compatible with these people, if for no other reason than to make it less awkward when you're drinking their recycled pee.
"So... how 'bout them sports teams?"
Hey, speaking of recycled pee...