And this goes to the root of the problem. 9/11 was a tragedy, especially for the victims and families/friends of the victims (deceased and survivors) but it did not (need to) "change everything." Terrorism was nothing new. Sneak attacks were nothing new. It was one novel (brilliantly executed by the bad guys) day, and now we are allowing that one day to define our society (and bankrupt it) because we choose to put up with it. The Depression and WWII generations went through arguably much worse. Arguably the UK went through worse in the 70s-90s with repeated domestic attacks. Not a single one of the screening measures you call "necessity" would have stopped 9/11, nor will they stop an equally novel and well executed attack today that threads its way through the vulnerabilities that exist in any system. What will stop attacks are good intelligence and investigative police work, all of which can be done within the bounds of the Constitution and without harassing millions of innocent travelers.

10x as many people died on 9/11 die in car accidents in the US every year. About 100x as many people die from smoking every year. Looking at pictures of 9/11 now evokes emotions that may or may not have been invoked 20 years ago by the same pictures without the context and personal memories. My kid (born 10+ years after 9/11) will look at photos of 9/11 the same way I look at photos of Pearl Harbor--historically interesting, but they don't make me want to go intern thousands of innocent Japanese-Americans. Making decisions on emotion hardly ever results in good decisions.