Consuming too much of any substance is dangerous. Even though cigarettes are more dangerous than marijuana when it comes to causing deadly diseases like lung cancer, the drug is still dangerous. Marijuana can still be a gateway drug to more powerful substances. Everyone's body is different, so one does not know how he will react when consuming large amounts of a substance. In short, yes, marijuana should still be considered dangerous.
The use of marijuana is similar to alcohol, it alters the perceptions and reactions of the body. So it is a dangerous substance, for example driving accidents are on the increase due to marijuana use in legalized states. And each person has their own tolerance for marijuana that may influence how they react.
While pure marijuana is not proven to be inherently dangerous on a chemical level, marijuana consumption can have some devastating long term effects. The increased laziness that is commonly associated with consumption can lead to poor life decisions, heartbreak, a falling out of societal standings, and other harmful things to oneself and one's society. Also, long term marijuana consumption has not been tested. There are new studies suggesting it can cause liver damage.
Marijuana as a substance is not inherently dangerous. There are some growers aiming to further and further increase the amount of THC in certain stains and for those with underlying mental issues I can see where it may pose a small threat but this is negligible compared to the dangers of alcohol and tobacco.