It's called security theater because it only gives the illusion of security: there are many examples where people have successfully brought knives, guns, explosives and what have you through these full-body scanners.
Further, it's theatric because the many of the "dangerous" items have no obvious malicious use, and the rules are totally arbitrary. I can't bring knitting gear on an airplane, but my small pocket knife is totally fine (according to official rules, though some airport security agents will disagree).
Finally, any attempt at plane hijacking nowadays will cause passengers to fight for their life to prevent it. Prior to 9/11 people would just sit still and wait to land in Cuba or whatever, but now people associate hijacking with flying into a building and will act thereafter.
It could actually be safer to allow knives and similar "weapons" that can't penetrate the plane body, so people have a chance to defend themselves when some terrorist inevitably smuggles aboard a handgun and starts shooting.
There are plenty of "weapons" you can take with you in the plane. I didn't realize the rules had been relaxed when I recently traveled with a set of kitchen shears in my computer bag. Leaving DFW no one said a thing. Coming back through CLE they searched my bag and found them. I expected I would have to toss them in the garbage, but was told they are OK being under the 4" limit [0].
There are a lot of "weapons" you could take based on the Tools category [1].
It's effectively zero, so yes. Taking the gun statistic in their blog [0]. Let's say they prevented a total of 5,000 noteworthy things ( that includes their gun statistic). I think that's a reasonable estimate given their figures.
0.000007656967% of the time they did something. In reality it's half of that. In reality of actual danger being present it's even lower than half of that. I'm talking near 7.6e^-8 in rarity.
The odds of being stuck by lightning is higher than the TSA ensuring anyone's safety.
A fun thing to look at is where those happened. Texas, Georgia, Arizona, Colorado, Florida, Tennessee. I did a quick search on each of these states, and they all have very liberal firearms rules. What are the odds that most of these were quite innocent mistakes? E.g. you always carry, and you forgot to leave it at home locked up.
I'm Canadian, but I have a similar story. I was travelling with my mother, and my backpack was swabbed and X-Rayed at security. No problems. It wasn't until I got home and was unpacking that I realized I had a bottle of aerosol nitroglycerine (!) in my carry-on! My mother's got a heart condition and I was carrying around a spare canister just in case something happened.
> Do you really think everything the TSA does is literally 0% effective?
Yes, for the purpose of "protecting American at large", it's approximately that.
And it's very simple to see too! The most effective way to prevent airplane terror is to stop everyone from traveling, are we gonna be safer thank to that, even disregard all the downsides of not being to travel? You know the bad guy can just plot their scheme elsewhere, right? What's next? Millimeters scanner at Taylor Swift concert?
Also, since this is HN, I believe your maths is incorrect. The effective rate is (100 - (100-x)(100-y)(100-z)...)%
It is literally 0% effective. At least for what they claim to do. What they do will only stop a dumb criminal, like one who couldn't even blow up his own underwear. But against any sophisticated terrorist, it will do nothing.
But is it a deterrent? For what? How many people are going out and hijacking or blowing up planes? Now, or before?
Pretty much all it does is waste time and money.
I'm not sure why people here keep referring to everything as security theater, to be honest.