"The Discarded" (1959) is a short story by Harlan Ellison.
A television adaptation, directed by Jonathan Frakes, aired on August 25, 2007 as an episode of Masters of Science Fiction.
The Discarded Wikipedia
This summary is based on the television adaptation.
A spaceship orbiting Earth contains people who have been banished from the planet because they are infected with an illness from Earth which causes disfiguring mutations. An ambassador from Earth, Curran (James Denton), travels to the ship and reveals that the illness has spread across Earth. A cure would require the blood of the discarded aboard the ship. He also promises the discarded that afterward they will be able to return to Earth.
An argument ensues. The leader of the discarded, Bedzyk (Brian Dennehy), who opposes all dealing with the Earth people who cast them out, is accidentally killed in a scuffle. His successor, Samswope (John Hurt), is the main proponent of donating the blood of the discarded so they can return to Earth.
The crew of the ambassador's ship extracts the required blood samples over the next three weeks, and then return to Earth. When the ship returns and the ambassador docks, the discarded are filled with hope and glee, happy that they will finally return home. Samswope conducts a 3-way marriage ceremony between 2 male and 1 female discarded. As Ambassador Curran enters the main room where the discarded wait with their luggage, his face is that of regret with an "I was just doing my job" expression, as many more newly infected people, brand new discards, enter the ship from behind him. Samswope cries out in disappointment, realizing his error in trusting Curran, something Bedyzk warned the discarded about before being struck dead by Samswope.
The scene then proceeds to the main living quarters, just as the story began, with the sound of banging, and blood splatters on the window. Samswope is committing suicide by repeated self injury to the head, just as an unidentified infected member did at the beginning. His body is then disposed of by command of the new leader. The moral depicted shows that no good can come without trust and unity, something that Bedzyk had preached, by instructing his fellow infected to refuse to help the "Earthlings", because of how they discarded them in the first place.