And then suppose somebody comes up with a way to do something useful, but it's an environmental disaster for the extra-terrestrial object under consideration. (Perhaps the word "environment" doesn't make sense if there's nothing there for it to be the environment of.)
For example, suppose that platinum was in short supply on Earth, and was desperately needed to make fusion power reactors work safely.
Would it be ok to strip mine Mars for platinum? Imagine total destruction of the planet's surface. But, humans get to live on Earth in a pastoral paradise. Is that ok?