[dekhn]

Your presumption is wrong. Science has shown repeatedly now that your assumption about carcinogens in marijuana is incorrect (I'd describe it as a "zeroth-order hypothesis", simply imputing properties by superficial similarity but no other evidence).

In fact, with the except of one non-invasive prostate cancer, marijuana seems to have a protective effect against lung cancer.

It still does cause respiratory health problems in heavy smokers, but not nearly as significant as tobacco smoking.