And why not, quickly breaking the passwords of some thousand of bank accounts in few minutes to get the appropriate amounts transferred in an additional few more.Practical quantum computers will be like dedicated GPUs, Neural Engines, and Crytpo Engines. It will be hardware dedicated to a particular task which it is exceptionally good at and a peripheral to a CPU to off-load special class problems for faster execution.
The CPU will still be there, and most computing will still use it.