As I read through the response to my initial post I'm struck by several points that confirm my own observation.
Security screening is variable, inconsistent and IMHO often appearing wrongheaded. No doubt experts will tell me that this is intentional, by keeping the bad guys guessing, but I don't buy that. What such variabilty creates is delay and crowding, and not infrequently, anger. The number of false positives sounded by those entry portals needs to be significantly reduced.
Articles have been written suggesting much of this passenger scanning is ineffective, that few real perpetrators are actually caught, but many legitimate travellers are inconvenienced. I have a fund of stories but I'll relate just two. 1). A few years back at IAD, huge delay in security caused by one individual reading every liquid container to ensure that the packaging read 100ml or less (Clearly no clue as to what that volume looked like). 2. In Orgeon, being wanded all over to identify why it sqawked when passing over my shirt pocket. Took him a some time but he eventally found it - it was the staple that held together the two pages of my flight itinerary!!!
I admit my security scanning fuse is short, especially short in the UK, and agree with those who've observed that 'attitude' is most prevalent there. I try hard to comply but have yet to receive satisfactory replies to the question "What caused the problem?" which I ask so that I can avoid delay in the future i.e. when I can get any reply at all.
Finally: I despair when some little old lady says to me "Oooh I feel so much safer now with all this security. Don't you?" To which I honestly reply "No, I don't". The 'Why' goes back to my statement above about crowding and exclusion.
If I wanted to cause damage and destruction why would I go to the bother of trying to pass through a security gate when I have possibly hundreds of potential victims waiting outside. Examples are many: In the Middle East examples of attacks on lines of personnel awaiting recuitment or pay cheques. Why attack a train when I can do more damage on the crowded concourse among those waiting.
You in the UK are very familiar with attacks outside secured areas (Manchester, Westminster Bridge, Borough Market). Ideas and Ideology travel quickly and very effectively and, it seems to me, most terrorists are today 'home grown' with little need to physically infiltrate a country via a commercial airliner. Drug smuggling, and what else, is being committed by those workers already on the secure(?)'Airside'. Hardened cockpit doors that can exclude pilots from regaining entry, anyone? The most egregious recent example being July 1st Canada Day Celebrations on Ottawa's Parliament Hill. In pouring rain 1,000's lined up for 4-6 hours and more, to get through to the secured stage show area. Why the delay? Security requiring the removal of rain gear for scanning, only two entrances all constrained by zig-zag barriers. Imagine someone creating a panic, wouldn't have needed any device, just how many would have been trampled to death. Clearly hundreds.
I submit that in many instances this overreaching effort at security creates the potential for far greater problems, and I ask the final question. "What actually is this excessive security trying to protect" The people or the show? The passengers or the aircraft? The people or the infrastructure? The politicians and their re-election?