Overdosing on weed has never been documented. I remember reading something like you'd have to eat 10s of pounds of marijuana to overdose.
People can get addicted to sugar and it can sure kill you slowly but it is far from illegal.
What is it about weed that makes it illegal? Besides disrupting major industries I'd say Terrence McKenna said it best: "Psychedelics are illegal not because a loving government is concerned that you may jump out of a third story window. Psychedelics are illegal because they dissolve opinion structures and culturally laid down models of behaviour and information processing. They open you up to the possibility that everything you know is wrong"
They spent all this time and money indoctrinating you and you think they wanna fuck all that up? Hell nah!