It has not been my experience that an employees commitment to safety has depended on which union they belong to, or if they belong to a union.
Given the issues with the FOD, tools, and other items found in the AF Tankers, I really dont think this is an issue of union vs non-union workers, or one location vs another.
Workers in Everett are hired the same way, the requirements are the same, and work their way through the union ranks. Training by Boeing remains the same at all facilities. It is the same techniques taught to install and fabricate the aircraft.
When they stopped accounting for tools was a big step backwards.
The memos that were shown by Aljazeera were not specific to South Carolina, but on the Dreamliner production everywhere. The Union is also protecting itself in Everett, but is likely another line of defense. Noting the issues with the AF tankers, those were built and quality control inspection by Boeing Everett and union personnel.
I have seen numerous posts here by people finding all kinds of stuff inside wings and fuel tanks.....
Production rates for an entire commercial aircraft, more than one a day on some models, is insane.