And yet, of those who actually did hijack the airplane using a gun or knife and who had taken over a US airliner, none were caught by US security beforehand.
This is because the security is all for show. Always has been. Still is. Take the case of the Syrian 'musicians' on Northwest 327. While these might be legitimate 'musicians' all but one were traveling on expired visas and the 'band' had published songs glorifying suicide bombings.
In spite of this, they were on a domestic flight inside the US. (Sound familiar?)
Security may well have deterred terrorists from attempting to hijack a plane, since the hijackers may have felt that the chance of getting away with getting weapons on a plane is lower if there are random searches.
Pure speculation. The record proves otherwise. The 9/11 hijackers certainly weren't deterred by security. Neither was Richard Reid.
I do not claim that the TSA is perfect. They are annoying and lots of the stuff they do is dumb, but I think it is dumb in a bureaucratic way, like all government agencies, but it is not evil and the folks who work there are not goons.
No, the TSA screeners are goons. (Faulty security for air screeners)
El Al security is much better, but to use those methods on all passengers at all airports in the US would be much more time consuming and much more expensive than the present system. It is all a matter of trade offs. We can argue forever as to what the proper balance between time, expense, and intrusiveness on the hand and safety on the other. I sure those kinds of debates go on all the time with in the homeland security department.
If it is a matter of trade-offs, then why did you write the following:
"Everyone potentially poses a danger. The terrorists are sneaky."
Either we're going to make flying secure or we aren't. But to say that the sham security in place is going to catch a terrorist is ludicrious. (Airport Screeners Do Poorly, Panel Told)