Everyone knew a heavier-than-air vehicle could never be built. And everyone knew a 250kt+ helicopter wasn’t possible. Yet many attempts were still made (and failed) at constructing such things, until eventually a solution was found.
Just because there doesn’t currently exist a solution that is cheaper and more efficient than a gasoline-powered ICE aviation powerplant, doesn’t mean that one doesn’t exist. But there will be many failures along the way.