At least they could add some variation to it, like replacing the grandfather with the grandmother now and then, or even the parents. And use castration or sterilization instead of murder.
Another example from Ted Chiang:
In his short story “What’s Expected of Us”, Ted Chiang gives an account of a futuristic world where a certain technological device seemingly demonstrates that people do not have free will.
This device, referred to as a ‘predictor’, has a press able button and a green LED light, which functions as a signal. The signal flashes if and only if the button is pressed. The interesting characteristic about this signal, however, is that it flashes one second before the button is pressed. This is made possible by a ‘negative time delay’ capacity in the predictor, which gives it the ability to send information backwards in time. The specific information that the predictor is able to send back is that the proposition ˹X presses the button at t˺ is true. This information is sent, from the future, to a time one second prior to the pressing of the button (which is the same time the information is sent), causing the green LED light to flash. Assuming the device is functioning properly, the information is sent (and the LED light flashes) if and only if the button is pressed it is impossible for one to press the button without the light flashing just prior, just as it is impossible for the light to flash and the button not be pressed. Any attempts on the part of the user to violate the above mechanistic principle, perhaps by attempting to wait for the signal to appear and subsequently refrain from pressing the button or to very quickly press the button before the signal appears, will prove to be futile.