As far as the Danger word goes... ok from my own experience...

When ds wasn't sleeping and DH and I were out of ideas we got every book available at the Library and perused them... I picked up SOS and by the time i had finished, I felt the words on the page reprimanding me as i was doing all the "wrong" things..picking him up, feeding him to sleep (in bed sometimes), rocking to sleep, etc etc. ...as a result i felt anxious and a bit disturbed thinking that i was the reason my ds wasn't sleeping and therefore the sleep deprivation was my doing.

From my experience, to a new mum who had very limited support I can see how reading her book could be classified as DANGEROUS- to new parents and their mental health.

Side note: thankfully it wasn't long at all before I learned to trust my mummy instincts and chucked the book.
Thats a really good point. A lot of parents are probably already emotionally on edge when they decide that they need some help and advice from a book and to be told over and over that you are doing the wrong thing could be what tips you over. And that would be for a normal situation and I can only imagine that it would be worse if you had PND. Now I am not saying that any other book is the best or anything of the sort, but I am saying that these books and others like it can be very very damaging because as parents, especially first time parents we do enough second-guessing of our abilities as it is, let alone having a book tell you that you are doing a crap job too by wanting to cuddle your baby!