As far as I am aware it's because FAA/DOT require flight/cabin crew to go through the same security point (i.e. the same entry point) as the pax.. This has been going up for some time before 9/11. I thought it was odd when I first came across it at US airports in 2000 and asked an American colleague at the time for the reasons.
Why the mockery? yes it wasn't right but pax. are also entitled to ask why have I to suffer a 12 hour delay causing me stress and inconvenience? which is clearly for whatever deeper reason irritated them all and caused the atmosphere, works both ways...situation could and should have been handled better...
Agreed BE standards of behaviour and civility from both pax. and staff appear to going down
For many years I was at the receiving end of pax. complaints and thought many were petty, silly, trivial etc. etc.
Now with a cargo airline and commuting on scheduled passenger services of a number of airlines I can see from the other side that many customer complaints are very valid both about the airlines and most of all about the airports, it's lots of little things that seem to add up and cause the upset and more importantly the stress. It is the stress factor that I believe leads to incidents such as this.