Politics usually prevents any valid science from being done on pot (by that, I mean no study is approved that isn't overtly trying to show it to be a bad thing). The funny thing is that science, being science, doesn't care about politics, and this sort of thing shows up. I know of at least one other study that tried to show high lung cancer rates in pot smokers. The results were nonsmokers and pot smokers having the same rate of lung cancer, people who smoked pot+tobacco a little higher, and tobacco alone a lot higher. Pot smoke does contain carcinogens, but it also has some cancer-fighting chemicals that cancel them out. It can also be vaporized or eaten, leaving out the bad stuff (mostly generated by combustion of plant material). Smoking is the worst form of delivery: Edibles have it beat in length of effect, and vaporizing is immediate and can be used for nausea where edibles (and pills) are self-defeating.
THC isn't the only active ingredient, there is a whole family of cannabinoids. Additionally, they can change how the body responds to terpenes (also found in the pot, as well as pretty much every plant in existence), which is why the pharmaceutical approach of isolating and manufacturing a single compound has always failed in replicating the effects of medical marijuana.
The idea of "needing an excuse" to smoke pot is a stupid one, because it implies that there's something morally wrong with it. As long as the side effects are less severe than the condition being treated, it's a legitimate medical reason. It would be nice if a non psychoactive variation could be synthesized, because not everyone wants to be high, but the cynic in me would see it being way to expensive for the 99%, while corrupt government officials use it as another excuse to double down on prohibition.