Be it debris, aliens, or more aliens, there are things in space that need to be destroyed.  At least, that's what the lineage of games leading up to SUPERVERSE would have you believe.  You know, they may very well be right.  Perhaps one day we'll be meandering out in the final frontier and come to the sudden realization that the universe really is out to get us, and the only way to ensure humanity's safety is to erase everything north of the mesosphere.