We do actually,its been used since 2000 BC in a medicinal way somif we havent worked outbthe long term effects it must be because those studying it are sitting around monged.Howard Marks was a smuggler,simple as,as gnasher said not a particularly good one as he was caught,but often thats due to all of the links in a chain,your only as good as the weakest,what makes Howard Marks different is he was a celebrity smuggler,a genial raconteur who promoted himself on the lecture/Tour circuit.
He smuggled cannabis,ansoft drug,not a gateway drug as is often promoted,that old chestnut has been squashed