Ya marijuana supposedly also leads to madness, extreme mental retardation, causes violent crimes and leads to drunken debauchery. Its also a gateway drug to much harder substances like heroin. Have you watched reefer madness?
You need to consider how much propaganda there is about marijuana out there. It is almost harmless except for a mild irritation in the lungs (still much better than cigs) and laziness. As for not preventing muscle growth, why the hell would they give it to cancer and aids patients then? I've heard of many pro bodybuilders that use it. It stimulates your apatite, leads to food consumption and increased muscle growth, or fat if your not careful. Don't believe everything you watch on tv.