Because if we imagine what it would be like to have super powers we might conceive of yet another feasible way to get them. So far we have X-ray vision, interplanetary communication, pointing at people and killing them, flight that can reach other countries and escape the Earth, and the power to wipe ourselves out in ten thousand washes of bright light and invisible death.
And by discussing the implications of such powers we can hopefully handle the day we get them. BTW, if you count manipulative psychology, charisma techniques and cultist indoctrination, we do have access to glamor powers. And by god can it be abused!