Why people shouldn't smoke marijunana?

Like tobacco smoke, it contains carcinogenic materials that get into the lungs and causes the same diseases that tobacco causes.

From BlergK: This answer is 100% true but does not disclose all the facts at hand. Smoking in general, regardless of the substance dictates one inhale the smoke of the burnt substance, this usually is mildly detrimental as this is smoke, a harmful thing to the human body.

Marijuana smoke contains different chemicals or lack of chemicals in most cases than the smoke of your average factory cigarette as cigarettes have many (up to 3000 or so) chemicals added to produce specific flavors. This doesn't mean that marijuana smoke is healthy but simply that it contains less included carcinogens.

On face value a person shouldn't smoke marijuana because in many or most countries it is an illegal substance. This of course does not stop people from using it as a medical or recreational drug due to the many beneficial effects it may have or the feeling it may provide an individual. In the United States for example, it IS illegal in most states or contexts, but no-one can prevent you from choosing to smoke it, much as a person cannot and should not force you to practice a specific religion (or not practice one!) if that is your personal desire.