I enjoyed the article, and it does a good job explaining SpaceX. However, it glosses over a lot of complicated things.

• Existential risk and the Fermi paradox: It barely scratches the surface on these as reasons why going to Mars is such an important thing for humanity. I assume most LessWrongers are already familiar.

• How to actually get to Mars: The $450 Billion price-tag he mentions is significantly inflated. That came from something called the "90 day report", which wound up just being a wish-list for all the big aerospace companies. When it became obvious how ridiculous things were getting, Martin Marietta put together a minimum-viable architecture called Mars Direct, which NASA subsequently used as the basis for their Design Reference Missions 3.0 and up. Basically, it's a $20-30 Billion program, spent over 20 years. Half the money would go toward 10 years of adapting existing technology for the job, and the other half would launch 5 missions with 6 people each spread over another 10 years. That's ~$500 million per person, for a round trip flight and a year on Mars. Using the previous mission's habitat module instead of bringing another one would likely cut the costs further. One of the original leaders of the design team subsequently expanded it into a book, called The Case For Mars, which I highly recommend reading. He starts firmly grounded in the near term, then explores options for eventually expanding into colonization, and discusses how realistic terraforming might be and calculates specifically what it would require based on current climate models.

And, while I'm at it, I'll drop a couple more links:

• More on SpaceX: If you want to follow the details, /r/SpaceX has a lot of intelligent discussions, and frequently leans toward more technical aspects with minimal fanboying. (People who tend to make overly optimistic statements are expected to have to justify them. For example, a running joke is that Elon's timescales are measured in Mars years, not Earth years, which certainly would explain a lot. SpaceX’s competitor, United Launch Alliance, is looked on much more kindly than Wait But Why makes them out to be.)

• More on spaceflight in general: http://www.nasaspaceflight.com/ has good technical articles on a range of topics, but they fund the site by restricting some content to "L2" subscribers.