A thin atmosphere is still very different from no atmosphere. If you have access to CO2 you can break it apart to get breathable oxygen, or use it as in ingredi

A thin atmosphere is still very different from no atmosphere. If you have access to CO2 you can break it apart to get breathable oxygen, or use it as in ingredient to make methane to fuel a return trip. If you have no atmosphere to draw on at all, then it seems like it's a lot harder to become fully self-sustaining. There is also something to be said for sending humans to a place where humans have never been able to go before. To many people, that's an end goal in and of itself.