What is that reason? Quantum mechanics is a well-established theory with multiple experimental confirmations, but also quantum computers already work.
Shor's algorithm working for large numbers would rule out some of interpretations of quantum mechanics like objective collapse, something that have not happened yet.
In any case my argument was not about any particular interpretation of quantum mechanics, my argument is that building quantum computer allows us to test our understanding of physics in conditions where it have not been tested yet. And so even if that did not produce any additional benefits the testing itself would be worthwhile.