How can science fiction explain why an FTL ship is not simply used as a planet killer?
Short answerUse arms-control rules, physical limits near planets, and the strategic value of habitable worlds, while recognizing that alien priorities may differ.
NotesSpace Carrier Avalon limits planet-destroying attacks through formal accords and rules of spaceflight. Other settings make FTL travel close to a planet dangerous enough to destroy the attacking ship. Planets also remain useful to societies that expect to inhabit them, although a species that lives elsewhere might have no such reason for restraint. Destructive attacks need not involve FTL: objects approaching light speed and antimatter explosions offer other possibilities.