Was it ever?
We say "The enemy carries the message". That's one of Kerckhoff's formulations of what is now more broadly seen as the Shannon-Kerckhoff and Dolev-Yeo models [0,1];
Assume that hostiles know everything about your technical measures except for your keys, and own every node on the network.
The further insight today is "Assume every device is hostile" and apply appropriate opsec (like keeping devices out of sensitive meetings etc). There are very few trustworthy endpoints unless you're capable of building and auditing them yourself down beyond the OS level to firmware and hardware.
In my observation the accusation "paranoid theory" is always propaganda from those who have an interest in breaking security, selling insecure products, or gaslighting others to avoid confronting their own denial.