That was a very interesting read. I've always been a bit skeptical of people who say we'll be living in space or colonizing other planets in the near future. I definitely want to read their book.

Also, this made me laugh:

And do you really want to create a group of hungry, disgruntled miners that are also able to sling very large rocks at the Earth?

That said, slinging large rocks back to Earth is the only way I can see them returning whatever they mine and that doesn't sound like a great plan either.