If there are other planets with life on them then humanity could be more like a plague, choking out who knows how many ecosysyems on however many planets, much in the sane manner we've done here.

If humans cannot develop a healthy balance on this planet - which is unlikely, as drastic population and industrial reduction would be necessary and right quick - then we do not deserve to escape this planet. Humanity spreading to other planets at this point would be akin to a disease spreading.