Yet without an enduring healthy, wealthy Earth economy the exploitation of other planets won't be possible. I think only a global economy of large scale and extensive interconnected capabilities can make and sustain the kinds of technology such colonies would require. I don't see how that could happen in sufficient time to provide any escape route from looming problems that threaten the health, wealth and durability of Earth's global economy.
I think asteroid resources for Earth's use offer some potential for economically self supporting (ie profitable, by trade) enterprise in space - and self supporting enterprise is an essential foundation to having something that will grow. Moon or Mars have no means to be economically self supporting during the establishment of a large, diversely capable independent economy. Even so I suspect any asteroid mining will be remote and robotic - going all out to avoid having to rely on astronauts, because nothing adds to the difficulties and costs of doing things in space more than using people. Possibly there will be something for astronauts in the near Earth operations to support more distant asteroid mining - like repackaging asteroid commodities for deliver to Earth. But even there the commercial imperative will be to avoid relying on humans in space.
I think asteroid resources for Earth's use offer some potential for economically self supporting (ie profitable, by trade) enterprise in space - and self supporting enterprise is an essential foundation to having something that will grow. Moon or Mars have no means to be economically self supporting during the establishment of a large, diversely capable independent economy. Even so I suspect any asteroid mining will be remote and robotic - going all out to avoid having to rely on astronauts, because nothing adds to the difficulties and costs of doing things in space more than using people. Possibly there will be something for astronauts in the near Earth operations to support more distant asteroid mining - like repackaging asteroid commodities for deliver to Earth. But even there the commercial imperative will be to avoid relying on humans in space.