I'm no fan of modern security theater but the number of plane hijackings and bombings in the 90s compared to today would seem to indicate that at least some good comes of it.
Although until 9/11 the intent usually was either to get to a non extradition country, or demand something from some nation state primarily.
The source above shows a clear decrease in airline fatalities through the years but I suspect that’s due more safety improvements through autopilots, better sensors, and more redundancy than the decrease in hijackings.
This is nothing to justify the massive surveillance.