why the hell use a planet that already has a unique ecosystem?
Because you're a kid that grew up inside his own poopy nappy - and didn't know any better?
Humanity as a whole is at a very primitive stage. We do things by instinct and by accident. We defecate in our own drinking water, fart and burn crud in our air. We seek to gain individual and personal advantage at the expense of the common good. We don't know WHY we're here, or WHERE we're heading.
I hope we grow up real soon...