Something about computers not being able to replace human judgment, I guess. But it all seems a bit paranoid to me. Daystrom didn't really have the wrong idea, after all–why shouldn't we build machines to do dangerous or boring work, to free up humans to do things of yet greater value? Is there some reason that starships must never be piloted by computers? There's no reason to believe that humans wouldn't have a place in space exploration, where appropriate, but unmanned vessels could accomplish much of that work safely and without wasting the time of hundreds of people charting empty planets. It just so happens that the Enterprise is one ship that pretty much always needs human judgment, since it's always getting into trouble. It wasn't a good choice of ship to computerize.