Earlier quoted context omitted.
Nobody dies from Marijuana overdoses but having smoke in your lungs is having smoke in your lungs whether it comes form a cigarette or a joint or a campfire and it's pretty much equally bad each way. Users tend to spend less time smoking joints than cigarettes but I'd be very surprised if the incidence of lung cancer from marijuana was zero.
it's not the tobacco per se, even if it's a factor, the primary cancirogens are the other shit they mix in to get it burning easily, reliably and timely
While you're probably right about primary carcinogens, the tobacco plant pulls radioactive isotopes like Po-210 and Pb-210 out of the soil and air, and those concentrations have been growing as Polonium levels rise in soil from years of fertilizer use[1]. So to say 'it's not the tobacco' is a very dangerous comment.
Moreover, cardiovascular disease is the primary cause of death for smokers, not lung cancer, and while extracting nicotine from tobacco and vaporizing it in a PG/VG solution might mitigate risk of the latter there's no reason to believe it'll do anything for CVD. If anything, without the MAOI in tobacco that increases the nicotine's effect, on average folks vaping probably have higher levels in their bloodstream than folks that smoke.