Scott Aaronson has offered $100,000 to anyone that can show that viable quantum computers are fundamentally impossible.
The question is not a practical one, there seems many technical difficulties that have prevented the primitive quantum processors being scaled up to working quantum computers. The question is deeper than this and asks is our understanding of quantum mechanics right?
What is true is that the scaling up of quantum computers cannot be forbidden by some obvious or trivial reason within quantum mechanics. So the bet is to come up with some convincing reason why practical scaled up quantum computers cannot be realised.