Not falsifiable?!! Don't bother me with details.
Quantum computing: the "Cold Fusion" of the 21st century.
Only difference? "Cold Fusion" was too easy to prove to be a hoax. So easy, that the president of my science/engineering university stepped in and said, "Stop this nonsense [cold-fusion research] RIGHT NOW. And I mean NOW, before you irreparably damage this institution!". No one would even dare to issue an edict like that on a subject which contains those two magic words: "computer", and "quantum".
THE MAJOR problem, and why billions and billions will be spent on chasing this unrealizable dream? It violates the most basic tenet of experimental and theoretical physics: IT IS NOT FALSIFIABLE.
Quantum computing, whatever IT is (ask an 'expert' to define what, exactly, quantum computing is), will only be abandoned whenever we find another digital rainbow, with its pot of gold, to chase.
How about "super-string" computers? ...Has all the makings of a concept guaranteed to bankrupt most smaller nations.