I doubt that is true, although I haven't seen any evidence either way. I guess it stops people indirectly, as any would-be terrorist has to be more creative, and in so doing probably alerts security authorities in other ways.
We all hate airport security, but without hard facts, it's very difficult to work out what you would use instead of TSA-style security.
There's without doubt a lot of people who've already done the "difficult working out", and not all of them ended up with "The TSA", or even anything vaguely similar.
(Can I point out that from outside the USA, while I greatly admire things about your civil liberties - it _astounds_ me that those same people put up with the TSA. I have no choice, the privilege of visiting requires it, but pornoscanners and gropings for domestic travel, and Kafka-esque no-fly lists? I can't quite understand how "the land of the free" ended up there...)
That's not TSA so much - on the contrary, TSA workers are, nearly without exception, pretty upbeat, efficient people enforcing rules they know are kind of silly. But Homeland Security as a whole is just one mistake after another, old-school Stalinist wannabes trying to bring back the good old Cold War gravy train.
Entering Europe, on the other hand? Nobody cares. Hi, you're here, need a taxi? Just the way America used to be.
Even including the 9/11 hijackings, your odds of surviving a plane hijacking if you stay down and don't antagonise the hijackers are very good as most of them have goals that does not involve killing themselves or the planets unless absolutely necessary.
A passenger plane carrying 1/2 of its fuel capacity damaged the Pentagon. 2 passenger planes carrying 1/2 their fuel capacity obliterated the WTC towers. This says more about the design of the towers, and resulting engineering shortcuts, than it does about the planes themselves. .
http://www.nytimes.com/2013/08/06/us/tsa-expands-duties-beyo...
While we do not have admission security to a mall like a plane the idea you are not watched in the mall and that there aren't guards around is a bit far fetched. You aren't searched unless you enter a store which has a bag policy because of a theft issue.
As for buses and trains, I am quite sure there are guards and cameras, just no oppressive searching of luggage or your person.
Once they can make it like "The Running Man" portrayed I won't have much of a problem with it but I don't think the tech is quite there yet
However, I accept your point that given the cost and inconvenience, it would be great if the TSA actually did notice.
The police report on crime too - why should those organizations be exempt from that?
The usual response is to keep repeating the same mantras to downplay the severity of these intrustions, not to substantiate (or worse, quantify) any of the perceived threats.