Great post!
To be fair, this usually doesn't start as a boggling level of disdain. It usually starts out as 100% ignorance. It's how the people and the group respond to the negative feedback from experts and from reality, which brings in the disdain, even spiraling to boggling levels.
There are two deep lessons herein, rooted in game theory.
EDIT: In this case, op did everything right!
Isn't it accepted security knowledge, that about 99% of everybody is at a "should not be doing it myself" level of security/crypto incompetence? I'm not saying that the example isn't particularly bad. It is.
Requiring competence would appear to be the wrong way to do it, here.
“There is no key.”
However, there's a problem when the severe danger is disguised by layers of abstraction and complexity and obscured by time. Even emotionally neutral warnings will trigger our psychological attack defenses in these cases.
Note, I'm not saying op did anything wrong. What I am saying, is that delivering negative feedback about anything complex is itself a complex operation!
A security membrane which needs this kind of feedback to work correctly should be viewed as having a serious design flaw.