Faldage opines: No one [even scifi proponents] seems to envision our ever having the ability to transport people off this world at a rate that even begins to match the rate at which we are overpopulating it. The answer can only lie in our stemming the latter.
If I may differ over a pedantic point. :o Heinlein in his work "Tunnel in the Sky" pictures an extradimensional portal that millions of people at a time can be herded through to another destination. In this small (from a popularity and size standpoint) novel, the Chinese do exactly that.
Now, I can't see it being done *today*. The logistics problems would be enormous, even if you didn't make any provision for the people on the other side. OTOH, any society that had such technology might be able to do something about the logistics problem.
For the future as I see it (and Heinlein too; he did "Tunnel" as a "what if" alternative to the flavor of his other books) is that space travel spells doom for the humans left on Earth. All the really adventurous types leave, aggravating by orders of magnitude the "marching morons" problem.