The biggest flaw in this film

I see what you mean, but the film doesn't really tell us one way or the other. It made more sense to me that the conspirators didn't want to leave to chance whether one of the astronauts would spill the beans because of a guilty conscience or resentment. It seems like it would have been an awful risk allowing them to live given that they were dead set against the idea and only agreed to it under threat of their families lives. That threat only held sway because their families were all together on a plane at the time that Kelloway first made his pitch. Once the astronauts were returned back to their home lives the conspirators would be at their mercy, unless their plan was to threaten them into silence for the rest of their lives (and if that was their plan it certainly wasn't a good one).

I am still trying to find something believable in this movie. Entertaining tho.

I think that was actually the most believable part. They needed to blow the lid open on the whole thing. So, they went where they know there are going to be cameras broadcasting to the entire world all at once. Nobody could possibly say they faked That footage.