Mrrzy wrote: "We have to be able to survive our planet."

It would be far more realistic to put all that time, effort and treasure into restoring and preserving our own planet rather than try to build an inhabitable environment somewhere out in space for billions of people and do it before we destroy the earth. Imagine the technology that could develop from the former endeavor, plus, and far more importantly, succeeding generations would actually have a place to live. But then it would be difficult and space travel sounds far more glamorous and intriguing than saving the earth.