SF is something fantastic that is still somehow supposed to be natural. Fantasy is something fantastic that is supposed to be supernatural. The reason that getting the difference right is that by definition real plausibility is better style in SF, whereas it is completely irrelevant to fantasy.
JK Rowling however attempts to explain the wizrds abilities in terms of a magic gene
or inherited trait. How is this different than the Q in Trek? In both cases, the supernatural is explained by using scientific principles.