I think the motive for Mars colonization is more robustness than efficiency. It'd definitely be easier to colonize the ocean than Mars. However, many planetar

I think the motive for Mars colonization is more robustness than efficiency. It'd definitely be easier to colonize the ocean than Mars. However, many planetary extinction events that would spare Mars would still wipe out settlements on the ocean floor, Antarctica, Mount Everest, or San Francisco. Asteroid impact, worldwide plague, nuclear winter, global warming, Chinese dictatorship, Terminator 3, Waterworld, The Core, Interstellar, they would all wipe out Earth while leaving Mars untouched. Even scenarios like Independence Day, Battleship, and Transformers would give a Mars colony time to react while the aliens were busy wiping out Earth, which might mean the difference between human survival and extinction.