True, a single-planet species cannot survive for long. Excluding costs, what if some natural disaster or human created catastrophe eliminates us all? Having a human population outside of earth would be like a backup incase something bad happens.
If by chance something tragic happens on earth, have another planet for backup, and if the sun somehow comes to an end, we just move to another solar-system such as Alpha Centauri etc.
But yes, it will cost a lot for such an endeavour.
If by chance something tragic happens on earth, have another planet for backup, and if the sun somehow comes to an end, we just move to another solar-system such as Alpha Centauri etc.
But yes, it will cost a lot for such an endeavour.