He didn't say they wouldn't be used, quite the opposite. He said there was certainty that if they were used, your opponent would respond with more of the same. This led to the doctrine of Mutually Assured Destruction from the Cold War.

Stated another way: if we use them we know they will be used on us, so we'd better not use them.

OP's point was the there is no similar guaranteed retaliation that might motivate restraint in the use of surveillance.