The road towards quantum computers have so many obstacles, which are deeply different and more challenging than the problems that we had with the development of classical computers. There are reasons to believe that quantum computers with a "large enough" number of qubits and low decoherence to be actually useful.
Yet, there are so many investments and there's so much research around that to suggest that the whole community believes that it's certain that we will have quantum computers sooner or later.
Where does this belief come from? Are there factual, scientific arguments to support that?