Mech assassin - far too simple - it would never catch on.
Just think of all the beaurocrats you'd put out of a job for a start!!
Just to add another anecdote to the lunacy:
In a previous life I held an ID for a BAA airfield in the London area. As part of my work I went to visit a colleague working in a Scottish airfield also within the BAA group.
When I arrived the BAA security official was happily filling out an escorted pass based on my owning a passport & being known to the staff member accompanying me. When I mentioned that I owned a BAA pass I was told I could no longer have a temporary pass but would have to contact the BAA at my home base and have them give clearance for me to access airside. ....oh - and I'd need to give 48 hours notice!!
I know security has to exist and have no problems if it keeps all of us secure, but this one really baffled me!!