I like what Whisper is doing, and deeply respect the crypto talent that went into building it. Personally, I think the soundness of the cryptography is the most important attribute of a cryptographically secure chat application. Other people think other things.
> They'll come around to your point of view in time.
The quote from Keynes was merely a slightly whimsical way to make the point that people can hold false beliefs for a very long time, and that it's probably better not to personally invest in the idea that they will come around by themselves in any specific timeframe.