The Space Trade is a book written on practical business applications for space development.

Whereas colonizing Mars is not desired or practical for business in the first place, trying to colonize Mars does not actually benefit anything. Its a gravity well with no resources worth extracting. Whereas asteroids are not gravity wells that you can blow bubbles with to create housing (space stations) from.

I'm not going to debate feasibility, because I have no theoretical basis on the subject, but I'm always excited by scientists who propose audacious projects. Mars has ice on its caps and gases in the atmosphere that could be collected, and the asteroids are rich in minerals and metals that could be extracted with new technology. The human species has only progressed technologically in history because of visionaries.