Was it set to 0000000? I don't know. Bruce Blair says it was, but doesn't have evidence he can/will give. A USAF official has denied it, but doesn't give evidence. Who is right? More importantly, who should we believe in such a situation? I don't think there's any easy answer to this. Personally, I don't think Blair just made it up. Along with having been a missileer himself in the 1970s, he also authored a report on command and control issues in the US nuclear force in the 1980s that was so disturbing that the Pentagon made it so highly classified that Blair himself wasn't allowed to access it anymore. So that's something. But it's still unsatisfying to have to say, "I believe it because Bruce Blair told me so." I have told Blair this about things in the past, and he doesn't like that I find it unsatisfying, but there you go. I have no doubt that Blair believes this is true. Does it mean it is true? That's a separate question.

What about the USAF guy? His response in my mind seems technical to the point of potentially posing the answer pedantically — "highly qualified", as you put it. And these systems change over time, and his answer is not especially well historically situated (exactly when did the conditions he describe hold is not clear). I also, to be honest, don't trust that the USAF guy actually has a good way to access that historical data. I have seen Congressional testimony where well-meaning USAF spokesmen have given totally false about past nuclear policy because the official internal records were wrong, and superseded by even-more secret directives (this was on pre-delegation of presidential authority, which is a separate but equally highly-classified and controversial issue). I'm not saying the USAF guy is lying. But he might be wrong, or he might be posing the answer in a way that is so narrowly constrained that it might be eliding over the big picture. I don't know.

Or he might be right, and Blair is wrong. Or they might both be wrong in some important way. It's hard to know. Welcome to the difficulty of trying to research command and control questions, where the answers are few and often contradictory and poorly sourced. (One of my current projects is to collect as much documentation onto these kinds of questions as it available, so we can at least see where different types of claims have been made, by whom, and when they contradict each other.)

As for the risk: you would in theory still need two rogue officers to start World War III. Not one. Though there are allegations (from Blair, Daniel Ellsberg, others) that many missile men figured out ways to subvert the two-man rule, and were proud of it (because they saw it as being something they'd only do in an emergency, for the good of the country, etc.). As for the risk: in principle it would make it slightly easier for a single rogue officer to have the nuke be launched. But there are still other complications (two-man rule sorts of things) that would make it hard to do. Not necessarily impossible. But hard.

The historical issue is, if it is true, about USAF resistance to requirements to make their arsenal harder to set off maliciously. This would fit in with a broader resistance to such safeguards by SAC and the military in general, in the face of urging by both Congress, the President, and the nuclear engineers at places like Sandia labs. The military people felt essentially insulted that their ability to train and screen soldiers was being questioned, and also feared that too many safeguards would mean that the nukes wouldn't be able to be used when they needed to be. This sort of thing would fit into that narrative very well. The denial of it is both about trying to reassert more responsible action on behalf of the military, as well, perhaps, of trying to discredit a frequent and well-respected critic (Blair).

For the broader historical context, see Eric Schlosser, Command and Control, or Scott Sagan, The Limits of Safety. Ellsberg's The Doomsday Machine has some other interesting historical "allegations" from a former insider.