Controlled legalization of other currently illegal drugs may or may not have benefits that can't be proven yet due to research of these drugs being illegal. There is empirical evidence that certain psychedelic drugs may reduce or eradicate opiate addiction. Even if these drugs were also addictive, it may be that the harm they cause is orders of magnitude less than opiates or similar. Replacing one problem with a lesser one is indeed a better outcome than what we have now.

None of this will be known, though, until certain deregulation and controlled legalization occurs.