Re: There's something missing here.
Reading between the lines it seems that the less experienced co-pilot wasn't trained by Scaled Composites in what would happen if he did unlock the shuttlecock booms during that phase of flight.
It may be he thought that he was just unlocking them ready to be deployed later, not that this would actually deploy them with the atmospheric drag under rocket power. It may be that he didn't know that deploying the booms under rocket propulsion could cause structural failure. Probably both.
This bit: "Virgin Galactic has added an inhibitor so its feather locks cannot be unlocked in certain conditions." suggests that either Scaled didn't know that structural failure was a possibility or didn't think that the humans on board unlocking the feathers at the wrong time was a possibility. This part: "[Scaled] identified that it did not have human factor expertise" suggests the latter.
If that's the case then the blame lies squarely with SC who obviously didn't know what they were doing. Which, when you're doing something for the first time is understandable I suppose. That said, a brave test pilot is dead and another badly injured because someone greenlit the flight without sufficient sanity checks.