How might Lem's objection be raised against "Harrison Bergeron"?
Lem's Objection is "The revolt against the machine and against civilization, the praise of the "aesthetic" nature of catastrophe, the dead-end course of human civilization-these are their foremost problems, the intellectual content of their works. Such SF is as it were a priori vitiated by pessimism, in the sense that anything that may happen will be for the worse."
In a sense I think that Lem's objection, as you have cited it above, is very relevant to this story. Note the way that "Harrison Bergeron" presents us with such a tightly controlled society that any rebellion is incredibly difficult to achieve and if successful, quickly stamped out, and eradicated incredibly violently. Even the little joy that the story gives us, when Harrison Bergeron declares himself to be the "Emperor" and begins to dance with his "Empress" with such beauty and joy, this is only a short-lived respite from the regimented nature of their society. For, when they defy gravity with their love and grace, it is precisely at this moment that Diana Moon Glampers arrives and shoots them both:
It was then that Diana Moon Glampers, the Handicapper General, came into the studio with a double-barreled ten-gauge shotgun. She fired twice, and the Emperor and the Empress were dead before they hit the floor.
As if to confirm this pessimistic ending, Harrison's mother is unable to remember seeing the death of her son on television and is just left with the physical reminder of the tears that indicate that she saw "something real sad," although she forgets everything else. Although we have been tantalised by the possibility of change, the pessimistic ending indicates that nothing has and will change as a result of Harrison Bergeron's rebellion.