The solution to our problems on Earth are in Space. Our future must be in space, or we may have no future. The most important reason to go to space is for survival. The Solar system is not a safe place. Even tucked in our womb on earth we are not safe.
Death can rain from the sky in a number of forms.
Both natural terrors, and manmade ones. This isn't as much of a danger as it was at he height of the cold war when this painting was made, but it is still a problem. As was made obvious two summers ago, impacts play a large role in the history of planets. That's clear if you look at the moon, you can tell that impacts were important. But Shoemaker-Levy 9 showed us they still play an important role in the development of planetary surfaces.