You do not validate a null hypothesis, you only reject it. Burden of proof is never on the theoretician. That's why the only scientifically sound statement so far on ghosts is "maybe".
If people could not come up with all kind of funky hypotheses in science we would hardly make any progress.
In theoretical physics the folks opposed to string theory commit the same fallacy by the way. It is not unscientific just because it is not testable yet. One day it might very well be.