As you have admitted in your post, that there is a none zero chance of humans becoming extinct. Don't you think it would be worth it to have some non-zero portion of the population and global budget working on ensuring our survival? Also, there are many commercial benefits that can be realized, not just idealistic ones. Mars has alot of deturium which could prove useful in fusion, it's lower delta V makes it a prime logistical hub for mining the astroid belt, etc etc. Read a plan for mars, and i think it will change your perspective.