Even if we somehow managed to not trash and pollute the planet to the point of no return, we would still be threatened and vulnerable on Earth. There are many things outside of the planet that could potentially wipe us out - for example, an asteroid. I like to see privately funded organizations such as the B612 Foundation work toward protecting the Earth from hazards such as asteroids. If we want to be able to go out and colonize other planets, we need to make sure our own planet, or our own species, is not obliterated by an asteroid, comet, or crazy solar activity in the meantime. I believe that a majority of humans got wiped out a little over 10,000 years ago, thanks to what is referred to as the "Clovis Comet." Another devastating series of impacts happened more recently, search online for "Bronze Age Impacts" or Estonia meteorite craters. Very interesting stuff if you have the time. Our species is vulnerable, and I hope we are able to survive and evolve for many millions of years!