- One rationale for Mars is In-situ Resource Utilization (ISRU). The particular opportunity for utilization that’s most commonly cited is to collect carbon dioxide from the Martian atmosphere. Carbon dioxide can be split to obtain breathable oxygen, though it’s not the most limiting consumable. The element that atmosphere processors on the ISS most routinely need to have replenished from an outside source is hydrogen. In combination with hydrogen, carbon dioxide can also be made into methane rocket fuel. It might be said that the best use for Mars is making fuel to leave Mars. That, in and of itself, is not a compelling reason at all to start a colony.
It becomes even worse when recognizing that there are far better places from which to obtain methane. The most common type of asteroid in the solar system is the carbonaceous chondrite, so named because it’s full of carbon. Significant amounts of carbon dioxide and methane can be present on these bodies, along with other useful volatiles like water and ammonia. While it’s technically feasible to export methane from Mars, it would be like exporting water from the desert.