It's legitimate and commendable to try to write your own cryptosystem, but winging it is not going to end well.
People can expect secure communications, just like they can expect lung transplants. They should should not expect either done by an amature rejecting supervision.
There was nothing wrong with what they wanted done, only with who was doing it and how.
* Writing a book = developing cryptocat.
* Knock it (writing the book) the fuck off = stop developing cryptocat.
* Real surgeons = cryptographers.
* Teach laymen how to perform major surgery in their kitchen = communicate securely.
If people "can expect secure communications", then, by your analogy, people "can expect to be taught how to perform major surgery in their kitchen". They cannot both be expected "to be taught how to perform major surgery in their kitchen" and not expect to have it "done by an amateur rejecting supervision".
Hence my amendment to the flawed analogy.
* Teach laymen to .... in their kitchen (ie, the shit that is hopelessly wrong about my surgery book) = the shit that is hopelessly wrong about cryptocat.
I think either works fine.