>Even given your maximum implausibility example of all silos ordered to launch all nukes, to get even one launched a number of people in the chain of command need to be convinced that risking the destruction of human civilization is justified.
IIRC there was even one such incident where a nuclear unit got some sent some routine training codes that turned out to be the codes for "launch against China" codes. They basically called back and asked to triple check the code and eventually it all got sorted out without any nukes being launched.
That was because erroneous codes were sent to one silo.
What happens when the correct codes are sent to all the silos?
So, you get on the phone, and call someone at HQ, to confirm the orders.
And they confirm that the orders are, indeed, correct. Command sent them down 5 minutes ago, and yes, we confirmed it.
What are you going to do?
If your answer is 'Not launch', you are not silo material, and have probably been weeded out long before you got to the point where you can ask this question.
IIRC there was even one such incident where a nuclear unit got some sent some routine training codes that turned out to be the codes for "launch against China" codes. They basically called back and asked to triple check the code and eventually it all got sorted out without any nukes being launched.