The problem is not so much the impact his lies will have on him or his reputation, but the social responsibility narrative and the lives of workers in places like Foxconn. Social responsibility is a difficult issue and it runs through many channels from rich western consumers all the way back to poor workers in China.
The issue is more that some will hear of his lies and assume that things aren’t that terrible. After all, if he had to lie to get his story how bad can it be? The opposite is also true and the fact he didn’t tell the whole truth could be just as destructive. Not everyone will hear that he made some of his meetings and evidence up and assume it still to be true.
He hasn’t just fucked up his own career he’s made it more difficult to tell the real story, the story without the reckless over simplifications or gross hyperbole.
Also, it will make the job of people trying to tell the full story, from all sides, much harder. If spokesmen or individuals with knowledge of the situation are thinking ‘what if this guy is like Mike Daisey and lies about it and I’m associated with the piece’ then how much and exactly what they are likely to tell journalists will almost certainly be tainted by Daisey and his lies.