Still on the topic of upsetting books

I've just read a book (Robin McKinley's "Deerskin") that contains descriptions of incest and rape and is a pretty upsetting book. It's not gratuitous at all, and while I have problems with the book, it explores a difficult subject, and one that needs to be discussed. But it made me wonder.
Are there topics, for example child abuse, rape, incest and so on, that are likely to be deeply upsetting to those who have experienced these things -- to the point that such books should have "trigger warnings"? Maybe something in the introduction or in the book description?
I'm not talking about the usual sex and violence type warnings -- guidelines to age appropriate reading and so on which I know has been discussed half to death.
For example, I've seen bloggers use the phrase "This post could be triggery" or "This post contains triggers" to give readers a headsup that they might want to avoid reading further.
It would be dreadful if books like Deerskin were banned, or for there be controls in place on how old you have to be to read it (how would that work, anyway?) but I do think that it would be a good idea to put something in the description to let the reader know what they are in for.
Or am I wrong?