I have most to say about his points 4-8, but let me open with a comment on point 13:
13. The interactions between alcohol and cannabis consumption, if both were legal, are unknown. Cannabis legalization could decrease the prevalence of heavy drinking and the damage it does, or increase it. This is not question that can be convincingly answered by abstract reasoning, or by information collected under prohibition. It’s an open empirical question, and – since the effects, for good or ill, of cannabis legalization on alcohol abuse could easily swamp the gains or losses with respect to cannabis use, abuse, and trafficking – the answer ought to matter.
Advocates of marijuana legalization often deploy the argument, isn't alcohol worse? The more polemical the exchange, the more bluntly this point will be advanced.
Let me rephrase that argument in a way that will illustrate what I think is wrong with it.
"Why are you so concerned about guns? Don't cars kill more Americans?"
The point is, you don't make a social problem go away by pointing to the existence of another social problem. Yes, as a matter of fact cars do kill a lot of people. Which is why Americans have invested huge effort over the past half century to improve the safety of cars, roads, and drivers.
Nor do cars and guns function in isolation one from another. Google "road rage" and "shooting" and you pull up 2.65 million hits.
Massachusetts police are hunting for the alleged shooter of a 16-year-old Maine girl who was struck in the arm while riding with her family along a major interstate in what authorities are calling a road rage incident.
The girl was traveling with her family on I-495 north in Merrimac, Mass., on Sunday when she was hit by a gunshot from another car. Witnesses told police there had been some sort of highway dispute involving the two cars.
Anyway, modern societies have no choice but to walk and chew gum at the same time. We can address the problem of gun violence before reducing the rate of automobile accident to zero - we have to, since the rate never will be zero.
I suspect Andrew will acknowledge the force of those arguments.
They apply in related ways to marijuana and alcohol.
First, as Kleiman notes, it's an illusion to imagine that marijuana and alcohol users form two separate and distinct camps. It's already true that many of those who drink too much also smoke marijuana, and ditto for many heavy marijuana users. I'll defer to Kleiman's warning about avoiding under-researched overstatements about these interactions, but they exist and could well become much more severe in a legalized world.
Second, as former Obama drug-control official Kevin Sabet pointed out in his bravura appearance on MSNBC's "Up with Chris," it's not as if alcohol law enforcement does not exist. In fact, as he notes, some 2 million arrests occurred last year for alcohol offenses (e.g. public drunkenness, drunk driving, and violation of liquor laws) - not counting actual crimes, such as assault, committed under the influence of alcohol.
Third, as with guns and cars, the trend lines on marijuana and alcohol are sloping in different directions. Alcohol abuse is becoming less of a problem for American society in the 2010s, marijuana use, by contrast, is increasing - and increasing particularly among the very youngest users, who should not be using it at all because of the harms to brain development.
Fourth, as with guns, so with marijuana, proponents misstate what critics think public policy should look like. The goal is neither gun elimination nor the arrest of every marijuana user. Guns are constitutionally protected, subject to reasonable restrictions. Occasional in-home marijuana use by adults is not something that any police department in America will bother with.
Fifth, in both cases, proponents and critics agree on a strategy of risk reduction. What proponents refuse to acknowledge, however, is that a legal regulatory regime is essential to risk reduction. It's because police could arrest a young man smoking marijuana in a park that they can effectively divert him to treatment instead - as more and more police departments do. Everybody understands that neither guns nor cars, neither alcohol nor marijuana, will vanish from our society. The key thing is not to make existing problems even worse. Which is what legalization of marijuana would do - a point I'll return to.