It obviously isn't. That's why there's a scale from A-B-C of harmful narcotics available to make things simpler for you to grasp.
Heroin and cocaine are clearly destructive over a long period of sustained use - cannabis, not so much. That's why decriminalisation and a defined line between it and them is necessary.
In that statement it looks like you are accepting that cannabis is destructive
The illegal drugs are all bad, just different in their effects. Do you know any long-term takers of illegal drugs? They turn into absolutely horrible people, particularly when their drug is in short supply.