How do you know? Again:
- Mother and Son
- She made the original pitch to Starfleet and was involved in the 'Genesis Cave' creation in ST:IITWoK
- Carol Marcus: "What we did there, we did in a Day..."
My point: She was definitely involved in the creation and testing. I seriously doubt David could have hidden it from her. Ergo: She knew and agreed to it get the Genesis Device working.
David said to Saavik ...(paraphrase)...
"I used Protomatter" ... He didn't say
"We used Protomatter".
He took complete credit for it.
I know we didn't get to see a lot of background on Carol, but from what we did see, I just don't believe that she would have agreed to use "...
an unstable substance which every ethical scientist in the galaxy has denounced as dangerously unpredictable."
As I said before, David indicated he did it to solve the major hurdle of getting the device to actually work.
His mother was the guiding force and face of the project to StarFleet, but it's pretty obvious to me that David was the 'Brains' of the project.
And it's also pretty obvious to me that his distrust of "the Military" didn't just spring up suddenly when they were unknowingly contacted by the Reliant with Khan in control.
He went into the project with that mindset.
(his mother even tells him she won't subscribe to his interpretation of Starfleet, which is another indicator of their ethical differences)
Once he figured out that protomatter would work and decided to use it, it's highly probable that he just kept that little tidbit to himself.
He wasn't going to let StarFleet in on it and kept it from his mom both due to that reasoning and because he knew she wouldn't have let him continue.
Anyway, that's how it see it.
