One big problem with Mars is that requires technology to live on. Most of the risks are civilization ending events not extinction level events. When civilizatio

One big problem with Mars is that requires technology to live on. Most of the risks are civilization ending events not extinction level events. When civilization fails, on Earth the survivors bang rocks together, on Mars they die. It turns civilization ending into extinction. One big question is if can make Mars civilization that would survive Earth collapse. It is possible that there are some things, like biological samples or advanced technology that have to come from mother planet. Mars will likely take a long time to become self-sufficient and until then it isn’t a backup. The easier self-sufficiency is, the less Mars is needed as backup. The final thing is that colonizing Mars could introduce risks. It would involve developing technology that makes disaster more likely, like advanced AI, genetic engineering, or moving asteroids in space. Or could be adding a place for conflict leading to Earth-Mars war that destroys both planets.