now we get to weigh the usefulness against the potential harm.Second, I'm sorry, but I don't agree with your principle. If I buy a kitchen knife, or even a fork, and harm myself by using it, is it really the fault of the knife ? It all depends as to HOW you are using it. Evidence of the majority of people over the world not being harmed by kitchen knife is not trumped by the few harming themselves with it, and even in the US, I don't think that people are suing firms producing kitchen knives.
we need knives to cut things (or scissors or blades of some sort) but these tools can be used as weapons. (Most tolls can and many of our favorite pole arms are farming tools). So then we bring this back to a D&D product (funny that is what we are supposed to all be here fore) and is the book as a tool more useful or more harmful?