The most infuriating thing about the whole sorry affair is that it doesn't need to be like this. LHR/LGW are pretty slick now (presumably they play by the same rules, if not, why not?) and like a previous poster said, passing through security in the USA of all places is a breeze!
No, it's uniquely a MAG culture problem in which this behaviour has been drilled into them from day 1. Treat everyone with contempt, even crew. This culture can also be extended to nearly anyone that works there, bus drivers, border agents. No-one seems to be happy. Couple that with inadequate staffing and overcrowding then everyone loses their rag quite quickly.
From the perspective of someone that must pass through this place many times a week this embarrassment compared to everywhere else is plain to see. Welcome to Manchester.
Glad I'm getting this off my chest, it's quite cathartic!