>So, I'd say its effect is very individual.
Not just the individual, though.
Strain selection is incredibly important for treating specific symptoms.
Having said that, the quality of the cannabis being smoked is moar likely to blame if the "user" for not having as great an impact. If the weed is shit, there are actually increased risks of negative "side effects".
A lot of that will boil down to the grower, which essentially means that for decades our government was criminally negligent for being so strict on citizens trying to grow their own medication, which created a larger market for cartels and "drug-lords" to assume the responsibility of growing said "weed". If someone is growing for money, not quality to treat medical patients (and believe me, the way certain states have been "regulating" the "medical" industry, it's mainly for financial gains), they might not always consider the "risks" associated with certain products or practices.
On top of the growers, environment in which the plants are grown are incredibly important, as well, to the quality of the product. Certain environments open the door for moar harmful things to thrive, which due to lack of proper understanding as a result of federal intervention which has prevented proper scientific study of said plant, are not always easily identifiable nor are they fully understood.
The main premise behind cannabis helping the immune system is, indeed, based upon actual science. However, because of the retarded retardedness of our institutions, they are not always "recognized" by said retards. Never-the-less, our body's endocannabanoid system is a "thing", and the organic compounds in cannabis work in tandem with human's, as well as all other animals, natural defense mechanisms.
One thing that is often overlooked is that just because cannabis does have beneficial properties naturally, it doesn't make us immune to all toxins or other harmful substances. For instance, if a plant is not properly flushed, there are residual chemicals that can exponentially increase the risk of negative "side-effects". Another serious harm could be done should the grower decide to spray plants to "protect" their crops from bugs, mildews, molds, etc. Depending on the product, along with several other factors, such types of "treatments" could pose considerable dangers to the consumers of said product. Could say lot about the subject, but the bottom lines really boil down to lak of education and inherent greed of society, along with several too many retards in charge for far too fucking long