Deployability is worth more than might be immediately obvious. The question of deployment is directly related to the business of availability. If 99% of people used a crypto system that provided no real security beyond thwarting a global adversary, which also had the option for further measures to confirm identity when necessary, we would be in a much better position than we are now because it would mean that when I do have contacts I would prefer to use encryption with the software will already be on their system and I only need to instruct them in how to use it.

There's a fallacy in saying that no measures are better than imperfect measures 'because then you don't have a false sense of security'. Regardless of security measures or not the false sense of security is baked into how people use computers.

I challenge you to go explain to anyone you know who does not identify as a 'computer person' how email routing works and why it's quite possible for a 3rd party to read their mail. If they even understand what you're talking about, the response is an almost universally cool 'Oh but so many other people do it, and what am I supposed to do stop using email?'

The vast majority of people will not stop talking just because in the abstract they might be overheard.

EDIT: As a note, I think any centralized system of key distribution is fundamentally insecure.