I agree that we just need to keep a secure level on flights, although I've come to a conclusion over the last few years. That conclusion is that either Terrorists are not smart enough or they just have an agenda that is being pushed by someone specifically on a specific target for whatever reason.
I'll expand a bit. For the past 5 years I've been travelling every 2 weeks using an airplane. Thats mainly within Europe. I've been to airports within Europe, specifically Santorini Airport, Mykonos Airport, Chania Airport where I've seen things going on that really doesn't make sense, nor it makes sense to my on why terrorist groups wouldnt prefer those kind of airports for their attack.
On Mykonos airport 2 years ago, Security check was handled by 2 young police officer in their very early 20's, no supervisor, no metal detectors no nothing. A wheelchair went ahead and they were trying to help the wheelchair to get front and they completely disregarded security. I wasn't searched or anything and I got boarded to a flight going to London. Someone could easily pass any kind of weapon in there. (The airport has since got renovated and prolly it goes with the European standards nowadays).
Santorini Airport 4 years ago to London, again flight going to London, there were so many people waiting and there was only 1 police officer in his late 50's trying to do security checks for hundreds of people. You understand how that system can fail. Again I got no checks on me or anything. Bare in mind both airports I am speaking of had no way to check cabin luggage for anything suspicious, it had to be done by the police officer looking into the bag, and that only was done if he thought that you could be carrying something. I saw him performing it once. (Again this airport has been renovated prolly keeps the European standards now)
Chania airport 1 year ago to Athens, they had around 5 security personel and 1 police officer. A friend of the police officer rocks up with a small hand bag, police officer silently asks him infront of me if he is carrying any firearms with him. He replies yes, gives him the handbag, passes through security and I saw his id he wasn't a police officer but a civilian, the police officer passes the bag behind the counters and proceeds giving it to him after the security check... (Nowadays I dont see police officers around the security but it did happen a year ago)
Thats only 3 airports I've been on and I've seen how easy it is to pass anything in an airplane and 2 of those airplanes were headed to London which is one of the big city capitals and targets. And I am pretty sure there are other places around Europe and other countries that the same thing is happening security wise. And if a civilian like me without resources can see those massive security breaches in a few of the airports he's been to, I am pretty certain that big terrorist groups with massive fundings and people everywhere cause they do have people everywhere, know about those security breaches. It still remains a question to me on why they never used those entrances.
P.S those 3 examples are from Greece, and well thats where I am from and thats where I use to travel a lot (back and forth to London) so thats why my examples are from here. Pretty sure other people have such examples to give.