I don't think that it's an argument against the flat earth. It's just a normal part of believing the earth is flat.
True, those who think that it's all about NASA and the US government, they are obviously incredible ignorant of the historical and contemporary scope of the science of it. But they too must fundamentally belive that it's some grand conspiracy, and that you can't trust anyone.
But that list includes
all international pilots, surveyors, navigators, engineers involved in large-scale projects, physicists and amateur astronomers.
Many are just ordinary people involved in running services, designing and performing construction work and amateurs pursuing their interests.
So, sure flat earthers must believe in some grand conspiracy and can't trust anyone, but to me, that sounds like a typical paranoid response.
In the end, no committed flat earther will be convinced by reason, logic or evidence. They just dismiss it all as irrelevant.
So, I believe that such a statement is "an argument against the flat earth", though not one that will be accepted by a
committed flat earther.