Everyone in the comments here debating the merits of Mars vs the Moon vs Titan seems to have missed the whole point of this article. The author is arguing that anywhere other than Titan is infeasible due to recent research suggesting that Galactic Cosmic Rays cause significant brain damage (not just increased risk of cancer). In fact, the article argues that the danger is so severe that even getting to Titan quickly…
Would living underground on Mars mitigate this?
The article author argues that underground living spaces are difficult to build and that Titan is therefore a better option, though personally I find that a rather unconvincing argument. Compared to the difficulty of getting to Mars, building underground habitats seems pretty straightforward in my uninformed opinion.