A humanity that destroys earth and is forced to move into space will be more successful overall, potentially, than one that does nothing on earth because we might harm the environment.

It depends what you count as success. Destroying your home planet and wiping out those who live with us here on Earth could be seen as less than successful. A neighbour who creates huge problems for everyone else on the street yet takes pride in their wealth and problem-solving abilities might come over as a little blind to their own problem-creating abilities. And that blindness might too be seen as less than optimal. It's not unreasonable to see "living harmoniously with others" as part of a good life.

This discussion turns us towards fundamental assumptions: is there such a thing as a successful life, and what is it? Does it belong to someone, or must it be shared? I hope we can be optimistic about these things, but we shouldn't underplay the suffering that capitalism, industry and technological progress have brought and their power to alienate us from our world, even as we celebrate their successes.

And, as thx1138 pointed out, the alternative isn't "doing nothing" but being considerate.