«The Burning Bridge» by Poul Anderson

The Burning Bridge is a science fiction short story by Poul W. Anderson first published in 1960.
A fleet from Earth is bound for a distant planet to colonize. Many of the colonists have left because of political and social discrimination.
Their travel has taken them far away and they are many decades out from Earth They are about at the midpoint of their journey and losing contact with earth.
Unexpectedly, a message is received from Earth which details a change in the social situation back on Earth ending one of the reasons for their departure.
Do they continue to the unsettled planet and suffer the deprivation and dangers of a new environment?
Usually there are two "reasons" why something is done; the reason why it needs to be done, and, quite separate, the reason people want to do it. The foul-up starts when the reason-for-wanting is satisfied … and the need remains!
The Burning Bridge first appeared in the magazine Astounding Science Fiction Stories in January 1960.
Poul William Anderson (1926-2001) was an American science fiction author who began his career during one of the Golden Ages of the genre and continued to write and remain popular into the 21st century.
Anderson also authored several works of fantasy, historical novels, and a prodigious number of short stories. He received numerous awards for his writing, including seven Hugo Awards and three Nebula Awards.