Micah Sherman, 32, and Nicole Graf, 28, who moved from Brooklyn to cultivate cannabis, care for the "mother plants," which will seed their 7,000-square-foot indoor farm in a warehouse south of Seattle, on March 15, 2014, in Olympia, Washington. (Gilles Mingasson/Getty Images)

California's marijuana legalization initiative is "horrible, awful, very bad no-good drug policy," said a leading marijuana expert who helped implement Washington state's legal market. That said, he'd vote for it, anyway.

Mark Kleiman, a professor of public policy at New York University, wrote this week that marijuana would become so inexpensive under California's proposed legalization ballot initiative, the Adult Use of Marijuana Act, that a dramatic rise in heavy marijuana use and marijuana-related disorders would be very possible.

Kleiman points to falling marijuana prices in Washington state, where the drug is already legal, as an example. He notes that some marijuana shops there are offering highly potent marijuana -- 18 percent THC -- for as little as $95 an ounce. He then does the math:

A typical joint contains about 0.4 gram of cannabis. $95/oz. is $3.50/gm. So a joint of “Uncle Ike’s Budget Bud” in Seattle has about $1.40 worth of cannabis in it. At 18% THC – aka “one-hit weed” – that should get three naïve users wrecked out of their gourds (if you’ll allow me the use of technical terminology) for about three hours each. That comes to about 15 cents per stoned hour, making cannabis far more cost-effective than even very cheap beer on a per-hour basis.

By Kleiman's reckoning, California's weed would be even cheaper than that within three years of legalization. This could be good for knocking out the illicit market, but there's a big downside, too: if pot is dirt-cheap, there's little to stop problem users from taking Dr. Dre and Snoop Dog's advice to "smoke weed everyday" quite literally.

Overall rates of monthly marijuana use among U.S. adults have changed little over the past several decades. But as Kleiman notes, some changes are happening within that group of monthly users: "In 1992, about 10 percent of people who reported using cannabis the past month reported having used it on 25 or more days that month. That number is up to 40 percent."

Kleiman worries that ever-cheaper marijuana could drive that proportion of daily users, many of whom meet diagnostic criteria for drug dependency, even higher.

Kleiman's criticism is significant, given the respect he commands in drug policy circles and his reputation as a radical centrist on marijuana issues. Many of the contemporary arguments against marijuana legalization seem like throwbacks of decades past, grounded in dubious argumentsmisuse of statistics and the occasional outright falsehood.

But Kleiman comes at the issue from a data-driven public health perspective. He's less opposed to legalization per se than he is to the fully commercialized markets springing up in Colorado and elsewhere. He says that a truly ideal policy might look like what we currently have in Washington D.C., where growing and giving pot is legal but selling it is not. He points out that there are a host of other legalization options between prohibition and commercialization that policymakers could consider.

Advocates of California's ballot measure point out that it contains funding for the prevention of teen drug use and additional law enforcement. They say that it will build on and strengthen regulatory measures recently put in place in the state's medical marijuana market. And the measure has drawn support from a wide array of politicians (including Democratic Lt. Gov. Gavin Newsom and Republican U.S. Rep. Dana Rohrabacher), public health groups (including the California Medical Association), and civil rights organizations such as the American Civil Liberties Union of California and the California NAACP.

Both Kleiman and the bill's backers agree on at least one thing: Given the current political environment, the measure is likely to pass this fall. Current polling in California puts support for legalization at about 60 percent, with 37 percent opposed.

Given all his concerns, I asked Kleiman whether he'd still vote for the California measure over the status quo. "Yes," he said, "unless there were some prospect of something better as an alternative."