A massive spaceship which was meant to colonize but now the people just travel between human colonies, and other planets, trading(?) Story follows a young girl, whose father is one of the councilors of the ship. The girl (name forgotten) and her friend, Jimmy, train for the trial into adulthood, which you either survive, that is a pass, or you die or fail to make recall, after being dumped on a primitive planet for several months. They go on trial, survive brutal treatment by the resident humans, and return to the ship as adults. Then follows a gathering of all adults, who decide to eradicate the planet. Girl voted against eradication. Cannot remember author, name or anything useful. One thing that stands out is the girl saying that no one cares about the spear bearers in a story, who are just there for the hero to kill.
This is the excellent 'Rite of Passage' (1968) by Alexei Panshin.
In 2198, one hundred and fifty years after the desperate wars that destroyed an overpopulated Earth, Man lives precariously on a hundred hastily-established colony worlds and in the seven giant Ships that once ferried men to the stars. Mia Havero's Ship is a small closed society. It tests its children by casting them out to live or die in a month of Trial in the hostile wilds of a colony world. Mia Havero's Trial is fast approaching and in the meantime she must learn not only the skills that will keep her alive but the deeper courage to face herself and her world. Published originally in 1968, Alexei Panshin's Nebula Award-winning classic has lost none of its relevance, with its keen exploration of societal stagnation and the resilience of youth.