> Regarding the health aspects of marijuana, we of course lack the wealth of knowledge that we now have on the detrimental effects of tobacco on pulmonary function and lung cancer risk.
Knowledge is potentially unbounded, but I wouldn't say we "lack" anything. Marijuana is probably the single most well-studied substance on the planet. Most FDA-approved drugs have gone through only a fraction of the level of study and testing that marijuana has.
> The experts with whom I have discussed this (a few pulmonologists) usually ask about marijuana smoke in the same breath as tobacco smoke, and consider it a probable carcinogen.
I've done a lot of research on this topic; unfortunately it's on another hard drive at the moment, but thankfully it's a very easy topic to research yourself.
Marijuana itself is not carcinogenic - in fact, it has cancer-fighting properties in some cases, and could be used as an aid in treating cancer directly, not just symptomatically. Consuming marijuana in edible or vapor form possesses no risk of cancer.
Interestingly, there have been a number of studies on heavy marijuana users (who smoke marijuana), and by and large, they have failed to conclude that even moderately heavy use of (smoked) marijuana can be linked to lung cancer. This phenomenon is well-known enough that it has spawned its own set of associated explanatory theories, and studies investigating those.
Obligatory XKCD disclaimer: https://xkcd.com/882/