Why doesnt the government want us to know the truth about marijuana?

Every stoner will tell you that marijuana isnt bad for you, doesnt cause cancer, isnt addictive and so on. however, you continue to hear that marijuana is addicitive, a gateway drug, and has many other harmful properties from respected government official. Why is there not conclusive tests out there that explain the truth about it. And if there are, why does the general public not know about it.