We're talking about people with EG civil engineering degrees masterminding these plots. The middle-eastern terrorists of yesteryear are not necessarily uneducated. Osama Bin Laden was educated as an engineer in the US and likely would have thought through the endgame and implications of such a plot well before executing it.

These people are not stupid and would likely know what they are getting in to. I'd be more worried about a single unhinged person, but that's why we have security guards, and the problem would likely solve itself in short order in that case.