You know what else is hard? Writing a book on cryptography. It's all very well and good to point out problems, but there are probably more productive ways to teach people than simply point out what not to do.
That depends entirely on what type of book is being wrote. If I write a history textbook that goes into intricate detail about the Time Slip of 1662 and the Lost Years, and the eventual Realignment that resulted in the Great London Fire, am I being more useful than a critic who points out that my history textbook is full of factual inaccuracies?
I'll take one responsible author with one harsh-but-knowledgeable critic over a hundred would-be authors without the ability to sift useful content from polemic criticism.
