And I'm not sure it's "helpful" really . It's more musing on whether or not this kind of advice is hurting more than helping. What you are saying amounts to "Crypto is really hard so use expert-authored solutions." But in my experience what people hear is "Crypto is Hugely Important and I'm using a expert-authored solution and using the same jargon, so you need to listen to me about all that security stuff and do what I say even though it's totally impractical."
Broadly, I guess I'm thinking that this creates little BOfH monsters, where a more nuanced, "big picture" frame might engender more thought about costs and tradeoffs.
Generally: I'm comfortable writing about crypto when the subject is "how you would practically break a system that makes mistake X or mistake Y". I'm not comfortable about posts with prescriptive content.
I am also not comfortable with posts that condone building cryptosystems out of primitives, even when they limit the solution space to well-regarded tuples of those primitives. If I had to write a prescriptive post about crypto, it would state clearly: you cannot DIY this, and you must use a vetted cryptosystem; your choices include NACL, Keyczar, and PGP.