At what point is it no longer tenable to say it was an honest mistake? What did the source have to gain from leaking the story? How do you avoid being used by s

At what point is it no longer tenable to say it was an honest mistake? What did the source have to gain from leaking the story? How do you avoid being used by some other source to plant a false story in the future? How do you avoid this source picking someone else to plant their next one? Is there really no way to balance "destroy all sourcing for other news" with "not be a patsy for WMD style propaganda?"