No, that is not how reasoning works. It is perfectly valid reasoning to begin by positing entities that we may not be possible to create, such as supersonic airplanes, coherent light, quantum computers, rockets that can reach escape velocity, black holes, or infinitely long lines that are perfectly straight and infinitely thin. Indeed, you might say that the ability to reason about the consequences of premises that we do not know to be true is the thing that distinguishes reasoning, as such, from simple parroting.

It could very well be the case that creating superintelligence is impossible. We won't know for sure unless it is achieved. Nevertheless, we can use reasoning from the hypothesis that it is possible to predict some of the effects that would ensue were it to be achieved. This allows us to easily dismiss the most profoundly stupid arguments, such as, 'Can you explain how exactly an AI would develop a novel planet-killing weapon without anyone noticing and pulling the plug?'

This reasoning, however valid it may be, is of course of much less interest should it turn out that we are reasoning about an impossible situation. Many arguments have been suggested on both sides of the issue, but the arguments for impossibility are extremely weak; most of them are conclusively dispatched in https://arxiv.org/pdf/1703.10987.