True, but working in teams is hard. The larger the team must be, the harder it is to recruit, train, organize, supply, maintain confidentiality, keep out spies, and avoid detection (hence the cell structure). Forcing terrorists to work in teams significantly increases the cost of conducting an attack, so it's an excellent security strategy.
That's an interesting thought. You're probably right. I imagine doubling the number of terrorists required probably more than doubles the chance of them getting caught. Might be exponential.
Unfortunately, one ziploc bag full of plastic explosive is probably more than enough to blast a hole in the side of a plane. And one of those beer belly things I would think could take a whole plane out.
