But if the answer is no--if we have no obligations to those imprisoned souls--then it seems there can be no moral objection to our trashing Earth, to the point where there will be no future generations.
If the answer is yes then we can go ahead and trash Earth. 
mnli hypothesis: If the answer is yes then we can go ahead and trash Earth.  premise: But if the answer is no--if we have no obligations to those imprisoned souls--then it seems there can be no moral objection to our trashing Earth, to the point where there will be no future generations.