The Federation's decision to ban the creation of synthetic life after Mars.
After the devastation of Mars in 2385 the Federation Council acted swiftly. Shocked by the loss and under pressure from a frightened public, it passed a ban on the development and use of synthetic life forms throughout the Federation.
The ban was broad. It halted work on androids similar to Data and shut down projects that relied on synthetic labor. It also canceled the Romulan relief effort, since the ships were being built with synthetics. Admiral Picard fought against the decision and argued that the Federation was abandoning its principles, but he could not change the Council's mind, and he resigned from Starfleet.
The consequences lasted for years. Synthetic beings were hunted or forgotten, Starfleet lost the trust of many Romulans, and the Federation lost some of its moral standing. The ban was a key backdrop for Picard's later struggles and for the story of the children of Data's legacy, such as Soji and Dahj. It was also a rare case of the Federation compromising its ideals in response to fear.