Were they though? Outside of the 69-71 era there were only a dozen or two per year. How many of those could be prevented simply by locking the doors and not giving in?
I've had significantly more damage done to my belongs because they were searched than what terrorists have done.
Why exclude the era where hijackings became so common that the authorities decided they had to implement security screenings to combat them? That seems like a rather relevant timeframe to me!
In that period, there was an average of something like 30-40 per year in the US. And air travel has increased substantially since then, so if we saw that rate today it would be more like 60-100 per year, or one every few days. Looking at it another way, about one in 100,000 flights were hijacked, compare that to the modern rate of fatal crashes of somewhere around one in 10 million to one in 100 million. (The number is very approximate because not enough crashes happen to get an accurate idea of the risk anymore.)
Now, hijacking don't have to be fatal, but they also don't have to be safe. Even a fairly small fatality rate (for a hostage situation) would catapult air travel from the safest mode of transportation available to the most dangerous. And people like blowing stuff up too. If anyone can build a big pipe bomb and bring it onto an airplane with no risk of being caught, the rate of exploding airliners would look more like that old hijacking rate than the modern rate of essentially indistinguishable from zero.
Airliners are easy and attractive targets. You get a lot more bang for your buck there. For example, the bombs used at the Boston Marathon would have killed a couple hundred people on an airplane, versus three people when detonated on the street.
I see no evidence that the increased screening measures since 2001 have helped things at all. But it seems crazy to me to argue for zero security. We tried that, it worked poorly, and basic x-ray machines and metal detectors cut the rate way down.
