All it takes is one civilization to shoot off their mouth and get destroyed by a much more advanced neighbor, in some way that doesn’t look quite natural. That will tend to confirm the cosmic paranoia.

I do agree with your probability assessment; I too think that the Prime Directive is a more plausible answer to the Fermi paradox, as is “we’re just alone”.

However, it is not necessarily the case that everyone suddenly gets talking as soon as one of them breaks radio silence. If everyone is silent because of a perceived possible threat, then it stands to reason they will continue to be silent even when they receive a message.