I think marijuana is not a harmful drug to certain people, but marijuana can lead to health concerns for people with mental issues. It can lead to depression and anxiety, most people think that marijuana is a harmless drug, but it can do damage. I think if marijuana becomes legal there should be warnings about its effect just like cigarettes.
Marijuana is not a dangerous drug likely to cause users to engage in risky or disastrous behavior. It's not nearly as physically disabling as alcohol. Long term physical effects of smoking marijuana are probably less than those of tobacco. Furthermore, there is no convincing evidence that legalization would even result in an increase in use.
Marijuana has been around for ages and we have yet to hear reports of health risks in the same way that we have about tobacco use. Tobacco and cigarettes are deadly, plain and simple. On the other hand, marijuana is used to help cancer patients and glaucoma patients. I'm sure that there are some reasonable concerns about recreational use, but it couldn't be any worse than the recreational use of alcohol.
The legalization of Mary Jane would not raise any health concerns. This is due to many people these days being knowledgeable about marijuana. It is not unhealthy at all and people realize this. Things like beer and tobacco are much more unhealthy that marijuana and we are able to stay on top of them.