There are no terrorists. At least, there are no organized terrorists. Attempts to thwart attacks by organized terrorist cells are a waste of effort, because there are no such cells plotting any such attacks. To say that TSA, as one example, protects us from terrorists is demonstrably untrue.
Let us assume, for the sake of argument, that there are terrorists just itching to blow up another plane. Thank goodness for TSA, you say; they prevent that by searching everyone at the airport.
Along comes a terrorist suicide bomber ready to cause death and destruction. She arrives at the airport fully-wired. She buys a ticket, then gets on line for her TSA pat down. She's 200th in line. The line moves and more people join the end. She's 100th in line. In the middle of the pack, she blows herself up, along with 200 random passengers waiting to be searched, 8 TSA agents doing the searching, and $4 million worth of expensive electronic gear. The police rope off the area. The FBI starts examining evidence, bagging body parts, and collecting DNA samples. This TSA inspection area, possibly the entire airport if it's small enough, is closed until the FBI is through with it and airport maintenance workers have cleaned up all the blood and gore and repainted the walls and ceilings.
Okay, no airplanes were harmed in the making of this terrorist incident, but several hundred people are dead and lots more are now afraid to be anywhere near the airport. TSA agents are rethinking their choice of careers. They got blind-sided by someone who hadn't yet been searched.
Why hasn't such an incident happened in the more than a dozen years since 9-11? There are a few possible explanations. One, there may be a critical shortage of dedicated suicide bombers; that would do it. Two, planning an operation that actually brings down an airplane takes years of work and lots of money; maybe they're broke. Third, the terrorists (we're assuming that such people still exist) don't need to do anything more because we're already terrorized; they have us where they want us; this is far more likely. This third possibility is actually the scariest of all. If true, the terrorists can simply disband and assimilate back into the population — mission accomplished, let's go home. I believe this is what has actually happened: they've lost their raison d'être.
If that's true, then TSA has no raison d'être either, except that they get regular paychecks. That's actually the only real accomplishment of TSA: they get paid for making us think they're accomplishing something. Protecting us from terrorists? Highly unlikely verging on 'don't make me laugh'.