Those have existed since the dawn of war, you can see deathtraps on certain episodes of Deadliest Warrior. There's a historical relevance at minimum in that. As well, anything can be lethal and most people already understand that at some basic level. It's not like this is new information that would be used specifically by those of ill intent. Can be used in other than illegal situations, for instance a surprise assault while camping, urban survival, etc. Life has an element of violence, I don't think there really needs to be a distinction. Legal violence exists and there are legal applications which can be found within either of those manuals, again; it's never legal to molest children. The two aren't mutually exclusive, bombs are based on multiple chemical properties and chemistry laws all of which must be met for detonation. I don't see why both aren't relevant as literary value. But this is not dependant on the subject matter which involves the commission of a crime. Possibly, but again there is only one intent that can be deduced from a title such as "How to Molest Children".
A bomb has a specific radius of effectiveness and a single use whereas a damaged child can become a menace to society without the proper mental treatment. I'd say a psychologically damaged child is much more destructive than a bomb. As well bombs usually are used for specific targets, I haven't pissed anyone off enough to have to worry about one, but a ****ed up human being? Different story. There is a vast difference between giving information that "could" be used in the two other books and that which most certainly will be used in the subject of this topic.