Illegal drugs, on the other hand, are harmful in small quantities or large quantities no matter what.
That is as true as saying caffeine is harmful in small quantities, no matter what.
Don't touch that coca cola!
EDIT: And illegal drugs can lead to crime.
Crime isn't a side effect of any substance. Crime is caused by the inability of some addicts to support their habit due to the drugs being prohibitively expensive because of their illegal status.
In switzerland where addicts can choose to purchase a supervised dose of heroin each day from regulated pharmacies for an affordable price, crime and disease among those involved in the program has been virtually eliminated.
I doubt that. People reach the point where they need so much to get the same effect that they overdose. And there will always be people who overdose because they're irresponsible eg. teenagers requiring their stomach pumped because they drank too much alcohol. Alcohol is legal.
To achieve a lethal overdose of cannabis or LSD is impossible. The LD50 of MDMA is unknown in humans, but it is estimated as being at least ten pills of the highest purity ever found, which is an insane dose.
And as riet says, this isn't taking into account the development of OD tolerance.
Anna wood died because she was misinformed about safe usage.