It also wasn't an uninformed decision. The FBI contacted Twitter and warned them that the story was false (a sensible guess at the time) and Twitter agreed to block the story.
Or created another problem. Like the FBI had the laptop, and could have verified it, but instead appeared to do nothing with it. Then there was the letter from '50 intelligence officers' claiming it was Russian disinformation.
Yet if the laptop and contents were real, and later verified. What does that say about the FBI and those officers competence, or political motivations? If the US intelligence agencies have ended up becoming the PR wing of the DNC, it's really not a very good look for the state of US politics. Or perhaps they've just gone back to their traditional roots and following in the footsteps of Hoover, Watergate...