Given that passengers have suspected terrorism from such things as speaking Arabic [1] and doing math [2] I wouldn't recommend gambling on the smarts of the dumbest person on a given flight.
[1] https://www.theguardian.com/us-news/2016/apr/16/southwest-ai... [2] https://www.washingtonpost.com/news/rampage/wp/2016/05/07/iv...
Tens of millions of people have flown without incident and you can point to two people panicking over stupid things? That seems like strong evidence against what you're claiming. People are simply not as stupid as you seem to think.
I'd say that's worse. Mobs are usually way dumber than individuals.
And if you're right, why aren't mobs of Americans attacking suspected hijackers already? Why didn't passengers attack the guy speaking Arabic or doing math? The evidence, based on millions of successful flights, seems conclusive: people are just not this stupid.