Where did you get the idea that marijuana is "pure"? It may contain the fungi Aspergillus, leading to the disease Aspergillosis in those whose immune system is lowered. Or the bacteria Salmonella.
You can read all about it here, Moldy Marijuana, The Straight Dope
"A variety of bacteria grow on damp Marijuana. Many are deadly. Researchers have found Klebsiella pneumoniae, Enterobacter cloacae, and Streptococcus (group D) growing in government-supplied reefer. Salmonella muenchen was found in Marijuana growing across the Midwest. Under anaerobic conditions (i.e., damp Marijuana stored in airtight containers), Clostridium species will rot pot; these are the famous boutlism bacteria."
"Some fungi won't rot pot, but they will put you in the hospital. Many fungi causing disease in plants die off after their host is harvested. Exceptions include Botrytis cinerea (the cause of gray mold) and Alternaria alternata (brown blight). After harvest, your competition becomes Aspergillus, Penicillium, Rhizopus, and Mucor, the baddest actors on the planet."
Pure marijuana, indeed!
Look, smoking marijuana is not safer than not smoking marijuana. Same can be said for cigs, cigars, crack, or anything else one CHOOSES to smoke. By and large, after years of personal research, I've come to the conclusion that inhaling smoke in any form is worse for me than not. BUT, I do think that cigs are worse to smoke than joints. My point is that to me it is senseless to treat marijuana and cocoa plants as the scourge of society while embracing tobacco.