Being around for thousands of years has zero bearing on whether something is good or bad. It can speak to relative safety. In all the thousands of years, there has yet to be a single death that can be attributed directly to cannabis (and I don't count "marijuana-related visits" to hospitals where regardless of which ailment a person has, if they test positive for cannabis it becomes a "marijuana-related visit", nor do I count deaths where a person just happened to have smoked beforehand).