That's where the failsafe comes in. The metallic archaea that corrode metal. It's the trigger that allows Skull Face to regulate the use of the gears. A tape explains that if someone actually tries to use it, a message is relayed by satellite to Skull Face and he decides whether it can be used as the client intends. If not, the metal-corroding metallic archaea activate and render the Walker Gear useless. He then dismisses the situation as a bad model and the client is none the wiser.Which is great, because in the events of Peace Walker (which Skull Face knows all about), the US is fully prepared to launch nukes, and it takes Big Boss himself phoning a guy at NORAD who happens to know him and can verify his identity to tell him that it's a false alarm, and the rest of the people in the room nearly shoot him for trying to stall for time.
Hot Coldman's entire plan hinged on humans being inherently unwilling to push the button, and he was wrong.
I imagine it would fall apart if everyone started trying to use their Walker Gears and all realizing they all had "defective" units.