"...while providing no substantial benefit."
I'm going to be pedantic and call BS on this one. If they hadn't been so bold and instead said "while in almost all cases failing to provide enough benefits to justify the cost" I wouldn't be making this reply.
Why am I upset about their hyperbole? Because it cuts into their credibility.
What's the specific counter-example I can provide? Read on..,.
In some societies, criminalization leads to social stigmatization even if the laws are not enforced or only lightly enforced, a stigmatization that would be absent or less strong otherwise. You see this in some parts of the United States, where the existence of little-enforced laws such as laws against littering, talking on the cell phone while driving, etc. reinforce and amplify the existing social stigma against such activities to the point that it's the stigma of being seen doing "the wrong thing," not the fear of getting a ticket or getting arrested, that drives people to follow the social norm.
Even if the enforcement of drug laws doesn't lead to reduced usage in and of itself, the stigmatization can.
Reducing the use of harmful drugs can benefit society in many ways, including fewer early deaths and fewer health problems.
The key though is that whether stigmatization by itself will lead to less drug use or not will vary from society to society and even sub-culture to sub-culture. A sub-culture which is known for being defiant of the larger society may in fact see doing things that are stigmatized by the larger society as a way to rebel. The 1960s young-adult/youth counterculture sub-culture in the United States is one example where a "main culture" stigmatizing an activity may lead to more, not less, overall use.
Now, does the existence of drug laws result in an enhanced stigma that leads to overall reduced drug use worldwide? I don't know. Is there someplace on this planet where drug laws are creating or reinforcing a stigma where the social stigma (not necessarily the fear of being caught by the police) is driving lower drug use? Almost certainly.
What's the bottom line?
* Don't summarily throw out drug laws worldwide.
* Do encourage every country and locality to ask itself to examine the totality of effects of its drug laws both within its own borders and on the rest of the world, and make an educated, informed decision about whether to change the drug laws to achieve the desired goals (which I assume are nominally a safer and healthier society, but which I sadly acknowledge may include things like keeping trading partners happy, keeping a dictator's friends flush with cash, and other factors that are irrelevant to the nominal purpose of drug laws), and if so, how.