Actually I am not sure on that. I have discovered tuns of evidence that smoking tobacco is bad for the lungs, but I found none for smokers of pure cannabis, nor for pure salvia divinorum (which is more recent, and so I have less data on it).<quoted text>I agree, smoking anything can't be beneficial for you. With that said, if you have a disease already, it can't be that harmful for you.
I have seen paper showing convincingly that the cannabis tar contains more dangerous carcinogenic molecules, in vitro, but that is not reflected in vivo.
Yet some art of smoking must be followed. The CO is easily eliminated by inhaling the right amount of air, and the fact that statistics on lungs diseases (or any disease) does not confirm the in vitro dangerousness might be explained by the curative virtue of cannabis. Smoking also allows the active molecules to go more quickly to the brain, without going through the digestive system, or the liver, which is often problematic.