Stupidity: When Flint Marko is escaping from the police, he climbs a chain link fence into a test facility. Besides having a chain link fence, there should have also been security cameras around the area as well as guards to prevent anyone from trying to get in. Plus, when the scientist notice on their computers that there's an increase in mass, one of them simply assumes it's a bird and then they continue their experiment. Instead of making assumptions, they should have halted their experiment and have someone take a look to see what caused the increase of mass.
Stupidity: After Harry threatens Mary Jane that he would kill Peter if she doesn't break up with him, she does what he told her to. Why didn't Mary Jane warn Peter about Harry? Did she forget that he is Spider-Man? Even though Harry was watching them, she still could have warned Peter.
Suggested correction: Mary Jane didn't forget that Peter was Spider-Man. A great deal of time passed between when Harry talked to Mary Jane and when she was forced to break up with Peter. During that time, Harry could have threatened to kill her family if she didn't cooperate with him.
Mary Jane doesn't take into consideration whether Harry would have the capabilities to kill Peter since Peter is Spider-Man.
Stupidity: Eddie Brock creates a fake Spider-Man photo and J. Jonah Jameson, due to his resentment towards Spider-Man, accepts it without question. Jameson should have inspected the photo before making it public.
Suggested correction: That is firmly within JJJ to do that. If being stupid about something is still in character and he would realistically do it, then it's not a mistake.
To add, after the physical confrontation between Eddie and Peter, when Robbie asks if there's a problem, Peter gives Robbie the pictures and then says that Jameson should have checked the sources.
Suggested correction: Jameson is not a forensic photographic examiner, nor does he have a photographic memory of the pictures that Peter sold him. It would take great knowledge of both for him (or anyone) to easily see the forgery.
