I'm a total noob here, so be kind...
I have always been confused why, when I am flying back to the US from an airport in South America, I have to go through a metal detector at the gate, submit to a check of my hand luggage, and surrender the bottle of water I purchased 5 feet away at an airport vendor. The surrender of drinks is what pisses me off the most, because on an 11+ hour flight it's nice to have your own drink rather than rely on the flight attendants' distribution schedule.
I've already gone through security screening to enter the terminal. Why don't they just ban liquids at THAT checkpoint and just let everyone buy food and drink inside the terminal?