Critics of Zubrin's accuracy don't seem to worry about it themselves.

1) Most of the Mars Underground's leaders are on the MS steering committee and have been since it's founding and two of the most well known spoke at the conference as they usually do. They are hardly distancing themselves from Zubrin as the author implies. Aside from the Mars Underground the current NASA administrator and the head of the human space exploration initiative (Scott Horowitz) also were members of the MS steering committee since its founding until accepting their current positions where it is inappropriate. Scott Horowitz has been a regular participant in MS conventions. But then all this data is inconsistent with the authors thesis that Zubrin is an isolated fanatic so why present it.

2) It is relatively simple to proivide real numbers when you criticize Zubrin's. The author simply handwaves them as outrageous rather than providing the numbers for actual comparison. Does he not know? Then he has hardly done a good skeptics job. Does he know, but not what to share? Hardly the proper protocol for a rational skeptic. Zubrin is aware of the criticisms and they have actually been tested in the analogue program. I think NASA's numbers have been proven conservative, but then maybe they should be. It's important to differentiate between minimum survival requirements and contigency allotments when discussing such debates.

3) On terraforming he seems to have missed the fundamental differenace between making Mars habitable for life and making it habitable for humans. These are vastly different time scales. But hey why bother to get your facts straight when a seeming contradiction can be used to make your preordained point.

4) Zubrin's justifications change little with time. He just changes what he emphasizes to resonate best with current events. I have never bought the stagnation arguement yet papers declaring it were still being distributed at the last conference. In my view it's not about going to Mars or stagnating it's about aceiving a higher level of innovation. Regardless, it's mostly about human survival and science that you can't accomplish with the alternatives the author blithely suggests.

5) The answer why Mars is very simple and not really addressed by the author. It's the easiest place to establish a permanent settlement off of Earth with plenty of valuable science to justify going there in the first place. If mankind can't live independently of Earth on Mars it can't do so anywhere else. No colony anywhere else on Earth assures the survival of humanity and/or technological culture in the event of potential planetwide disasters.

see ya