Context. And more context.
Or at least seems to induce a fair amount of magical thinking. And that would be magical thinking not a hell of a lot different than claims of magical gods, psychic phenomena or the belief that vaccines, cancer drugs and many other medicines are actually poisons being peddled to unwitting consumers by the evile of Big Pharma. People who rightly mock conspiracy theories about 9/11 and new world order, secret governments, turn around and make the base assumption that none of the evidence showing that cannabis has more than negligible deleterious effects can be true, because there's a government conspiracy to hide the truth and scare the masses.
There is fairly exhaustive evidence that indicates the legal status of cannabis is absolutely absurd and that the scare tactics engaged by most public agencies is vastly overblown. That is not to say that there isn't risk and evidence for harm stemming from cannabis use, on many different levels.
There is no question that smoking anything causes respiratory damage and damages cilia in the upper throat. Anyone who has ever cleaned a pot pipe knows that the tar left behind is impossible to clean off with water alone, unless it's boiling - this same tar mattes the cilia in the esophagus and like tobacco, coats the lungs. While the average cannabis smoker, smokes less than the average tobacco smoker, thus lessening the overall damage of smoking it, the tar that is formed is actually worse weight to weight, than the tar from tobacco. There is a great deal of evidence indicating that cannabis smokers who do not smoke tobacco have a higher incidence of bronchitis and chronic bronchitis, than non-smoking populations.
No links have been found between cannabis smoking and lung cancer or emphysema - though there is evidence of proteins that are thought to be precursors to cancer in cannabis smokers, there is also evidence that cannabis use may inhibit the development of those proteins into cancer. It is important to note however, that there is no evidence that it impacts the incidence of cancer in concurrent tobacco smokers.
Reproduced studies have indicated that the incidence of cannabis addiction in cannabis smoking populations is around fifteen percent. Addiction being defined by the DSM IV criteria, a conjunction of pervasive use, in spite of significant personal harm. Cut that by a third to be certain you've weeded out biased diagnosis - cannabis is magical you know - and you still have one out of every twenty cannabis smokers addicted at some point in their life. When we look at populations that use cannabis and also have concurrent neurological issues, the percentage skyrockets. And it is very common for people with neurological issues such as ADHD, bipolar, schizophrenia and other psychotic disorders to use tobacco, use cannabis and other illicit drugs.
I could go on and on, but here are some articles that do a much better job than I. I am way too busy at the moment and will get to more evidence - recent studies and the like, when I can. These peer reviewed journal articles and reports are not protected by pay walls and easier to throw out there, because you can read them and I don't have to summarize anything. I don't have the time to summarize material that is paywall protected, I'll get to it asap, but I am trying to get through a lot of credits this summer and it's more than a little stressful.
A Lancet Seminar.
The 2001 Australian study on the health effects of cannabis use. I suggest looking at the summaries of each section and then looking at the body of each section, if you have questions.
The British Journal of Anesthesia.
The British Journal of Psychiatry.
This wasn't hard to find folks. And this is just what I looked for to throw something up that isn't paywalled. Are we to believe that there is some conspiracy that is trying to toe the usual line of most public agencies in the U.S. Oh shit, I'm sorry but are we to believe that there is some government conspiracy to contradict the usual line of said public agencies?
Of course there is, because I just keep forgetting that cannabis is fucking magical. Sorry, I'll try better to keep that in mind from now on.