answer:Spectacle. The idea isn’t so much to destroy the insubordinate planet, but to send a message to the others that insubordination will not be tolerated. The exact method is a hairy question. It must be visually compelling (the destruction will of course be televized on all propaganda machines on all subordinate planets) but not give the impression that I’m doing this for emotional reasons or that it is anything more difficult or important than swatting a mosquito. The Genesis Device would do well, I think, if I had it. Instant removal of all annoying life forms, and leaves behind a nice, freshly terraformed planet. Perhaps for use as a penal colony?