A lot of these sites are derivatives of the old "Anarchists' Cookbook" and other such nonsense. A good proportion of the material is simply wrong. Some of the rest is so dangerous and stupid that one does not have to worry, because anyone attempting the recipes will not survive to hurt anyone else.
The Kewl BoMZ kids will eventually solve the problem when the ISP's who host the sites are sued into oblivion by bereaved parents.
Read the newsgroup alt.engineering.explosives sometime for a horrifying example of irresponsible misinformation and technical incompetence by people who never passed High School Chemistry.
The thing is, a recipe so stupidly dangerous that the person mixing it won't survive is just fine for Mohammedans who have accepted Sayd Qutb's reinterpretation of Islamic 'martyrdom' as including suicide in the process of killing infidels: just mix a batch sitting among infidels at 35,000 feet.