First part here.
One of the best bets to fly cheaply off Earth is a space elevator, but there are many proposed designs not involving impractical rockets: skyhooks, theters, launch loops, fountains (these are, I think, particularly promising if coupled with efficient and clean energy sources, because we can realize them with the technology available now) and even orbital rings. For some of them we don't have yet discovered suitable building materials or techniques, but others lack only political and financial commitment.
Why don't we start thinking seriously about these technologies? Why are we not interested in the enormous, life-changing possibilities laying outside the thin layer of gases above our heads? The world economic potential is and will be immense while its resources are not yet depleted, and could be put to good use instead of being wasted on territorial squabbles for small change, that benefit only an insignificant fraction of the population. There is profit to be made in space, a lot of it.
This is one of the things that really baffle me: capitalism is always looking out for profit, isn't it? It's what it does, it's what it is. So how comes that it has not yet risen to the challenge? Political opposition to huge project without visible immediate benefits is strong, but I think that's not the issue. Politics never stopped a businessman running toward the money: twisting viciously the arm of a government of choice behind its back is the daily morning warmup for any serious international corporation.
Maybe they still don't realize what's out there.
Take Luna as an example. We've already been there. It's easy to reach, it requires only three days. It has an area of a quarter of all Earth's landmasses, a little smaller than the Asian continent. That's a lot of space to build colonies, labs, research facilities, factories, even sealed farms. Maybe we could live off the land, if we get good enough at engineering. But even without that, with regular support from Earth we could turn Luna into a second world to inhabit. It presents a lot of advantages. Its reduced mass means a shallower gravity well, so we could launch spacecrafts to the outer planets from there. It could be useful to produce materials not achievable on Earth.
Luna is not a rich world, because without tectonic activity it's quite hard to form ore deposits, but up there we can still find hydrogen, ammonia, methane, mercury, sodium, silver and even water, if only we find an economically viable way to extract them.
Mars is a better candidate. More massive, farther, but immeasurably more valuable for colonists. We should think about ways to terraform it, to make it suitable for human life. Many methods have been conceived to reach this goal. We can add water and change the content of its atmosphere (and its spin or tilt, if we want it) by slamming cometary bodies on it. We can seed martian soil with genetically engineered lichens and plants to help the building up of oxygen, we can induce a greenhouse effect to increase temperature. We managed to do the latter on our planet, in only 100 years and without realizing it: why not on Mars, willingly? It could really be a place to live on, and once a significant chunk of Earth's population is transferred there (or once Mars citizens start having children) we won't have all our eggs in one basket anymore. We will be able to draw a deep breath... and go on.
Humankind will eventually be relatively safe from accidents and the wondrous thing is that this is not our only chance. We have a variety of choices, of intermediate steps to take.
(to be continued... )