Now, I understand that this would just be speculation on completely unfounded principals, but why would a former worshipper of Sanguine/Daedra trafficker consider this book supposedly written by Mehrunes Dagon to be dangerous to handle? Remember, it'd have to be specialized knowledge, but not too specialized so that someone who did not worship Dagon directly could know its danger.
I suppose as a corollary to this, what do you suppose the Mysterium Xarxes is to someone who is not a part of the Mythic Dawn?
I want your wild theories and speculations, don't worry, it's for a good cause.