Should also be noted that we need to realize that security is a trade off, same as safety. There are many things we could do to make airplanes safer, but most of those don’t make it that much safer.
Ultimately, nothing is 100% safe, and we need to calm down about some things. You are far more likely to die today from a mechanical failure in an airplane than a terrorist attack. It’s possible to sneak (whatever) past security and blow up a plane, but the odds of that happening are so incredibly low that spending additional money to increase the effectiveness of airport security is not necessarily a good use of money.
I see THz scanners as a way to decrease the cost of airport screening by reducing the number of people who have to be on-hand, and speeding our way through airport security lines. As long as the privacy concerns are properly handled, I don’t see a problem with it.
The savings from that should be put into police resources to increase their ability to find people who intend to do harm, and into preparedness work (which helps no matter what the attack or natural disaster is).
In short, we cannot prevent 100% of disasters (manmade or natural), but we can put resources into preventing as many manmade disasters, and resources into recovering from manmade and natural disasters as quickly as possible.