What you are describing is inverse vandalism. If we ignore the problems of here and now, the realization of a future where we colonize the stars may never occur. Obligatory quote:
Yeah, yeah, but your scientists were so preoccupied with whether or not they could that they didn't stop to think if they should. - Dr. Ian Malcolm.
Our focus should not be on whether we can do something. We should carefully consider why we are doing something and ensure we aren't acting in a self-destructive way.
As odd as it may seem, the human race is fully capable of accomplishing both space-expansion efforts and cleaning things up here on Earth. More than that, space opens the door to a wealth of possibilities for ameliorating or even solving many of the major problems we face today. That includes environmental efforts and energy production.
Even if we were to pursue a massive space race, it'd only consume a relatively small fraction of humanity's industrial capability and resources as they exist today. In the context of a long-term terraforming effort, after a significant space-borne industry has been created, these sorts of binary comparisons become all the more laughable.
You act like there is some master-judge who will tell us what we should do that will give different results from our own introspective desire to do exactly what we want. We should do what we want to do, and there is no such thing as vandalism outside of human created law.
Yeah, yeah, but your scientists were so preoccupied with whether or not they could that they didn't stop to think if they should. - Dr. Ian Malcolm.
Our focus should not be on whether we can do something. We should carefully consider why we are doing something and ensure we aren't acting in a self-destructive way.