I can't stress enough how wrong this is. The majority of mediocre programmers will take anything written in a book as gospel. When their boss tells them to encrypt the customer data, there is a non negligible chance they will go straight to a cryptography section in a book they read and copy it.
There is no positive value in that section. Readers will only be hurt by it.
This constant scare tactics and putting crypto on a needless pedestal is counterproductive as it may well turn potential learners off. It may be complicated but people learn complicated things all the time. No one is born an expert.
To contrast, writing crypto as a hobbyist isn't dangerous, but using someone else's bad crypto can be dangerous indeed—because it's almost never clear that the crypto within the software you're using was written by a hobbyist.
People can learn crypto all they like. In private, sharing their learning with peers and/or mentors. But their "homework projects" should never be posted on the public Internet where they could be found by people looking for professional solutions, any more than a chemistry student's homework project of devising a work-up for making non-volatile explosives with volatile intermediaries should be posted on the public Internet where it might be treated as a safe, well-known procedure for doing so.