I've read a few of his books. I agree that space travel is necessary to ensure the survival of our species.

There are too many factors that guarantee the destruction of life in the planet or creates a reset for evolution to start from zero.

At the moment it's humans doing a pretty good job through fossils fuel that are likely to destroy human life but it won't kill the planet I don't think. Earth will reset eventually and other life forms will thrive under different conditions. This is the most immediate problem.

After that then we a whole variety of possible planet wide destructions that are like to happen before eventually the sun dies out. So space travel is necessary if we want to survive through time.

This can only happen as more and more people think outside of their own lifespan.