I doubt they started off just waving the guys through. Most likely they started off doing full screenings, but, as I've said multiple times, it wasn't worth spending the time processing them, just to give them back the most dangerous thing they could carry. Basically, the lines got too long and people complained about the long lines, so they got rid of the thing that caused the long lines in the only way they could. Because the appearance of security is in itself a form of security. It's the same concept as having a sign for a home security company in your front yard without actually having the system for that company in your house. Robbers will look at your house, see the sign, then move on to the neighbor's house because your house looks more difficult than theirs.