"For me the real evil of masturbation would be that it takes ..." — C.S. Lewis quote meaning

For me the real evil of masturbation would be that it takes an appetite which, in lawful use, leads the individual out of himself to complete (and correct) his own personality in that of another (and finally in children and even grandchildren) and turns it back: sends the man back into the prison of himself, there to keep a harem of imaginary brides. And this harem, once admitted, works against his ever getting out and really uniting with a real woman. For the harem is always accessible, always subservient, calls for no sacrifices or adjustments, and can be endowed with erotic and psychological attractions which no real woman can rival. Among those shadowy brides he is always adored, always the perfect lover: no demand is made on his unselfishness, no mortification ever imposed on his vanity. In the end, they become merely the medium through which he increasingly adores himself . . . . And it is not only the faculty of love which is thus sterilized, forced back on itself, but also the faculty of imagination.