Everyone has the right to commit suicide. However, that doesn’t mean that the government doesn’t have the right to make certain suicidal behaviors illegal for reasons of public interest. If heroin were legal for adults and were no longer an “outlaw” substance, more children would gain access to it and try it.
Following that logic, we could ban any item that might harm unsupervised children.
Guns, cars, antifreeze...the list is endless!