Zubrin has no time for anything that does not lead immediately to a Mars mission, which makes him rather annoying. He dismisses a return to the Moon on the basis that there's nothing interesting there; blows off development of VASMIR, an engine which could reduce travel time to Mars by an order of magnitude; and states that the ISS has "no rational purpose". I don't agree with his characterization of any of these things. Yet as to his goal of making us a true spacefaring species, I am in complete agreement.
The American people want and deserve a space program that really is going somewhere. But no goal can be sustained unless it can be backed up, and not by "rationales," but by reasons.
There are real and vital reasons why we should venture to Mars. It is the key to unlocking the secret of life in the universe. It is the challenge to adventure that will inspire millions of young people to enter science and engineering, and whose acceptance will reaffirm the nature of our society as a nation of pioneers. It is the door to an open future, a new frontier on a new world, a planet that can be settled, the beginning of humanity's career as a spacefaring species, with no limits to its resources or aspirations, as it continues to push outward into the infinite universe beyond.