Smoke is fundamentally bad for the body. Even though there are some benefits of marijuana, smoking anything damages lung tissue and can lead to cancer. Smoking small amounts is obviously less dangerous, but there is no denying that smoke is had for human health. It's more likely to get lung diseases if you smoke anything, be it tobacco or marijuana.
If one is to smoke it from a pipe or something along those lines, then yes, the intake of it could be harmful. That would be the smoke inhalation, however. It would not be the marijuana harming the user, but the way it is being taken in. It's sort of like how you can get aspirin anywhere, and it's relatively "safe", but take 30+ grams of that and you'll probably have your last headache.