Democrat Dianne Feinstein, California’s senior U.S. senator, has thrown her weight behind the effort to defeat Proposition 19, the Regulate, Control and Tax Cannabis Initiative of 2010. Apparently Feinstein believes that California’s present pot prohibition, which was initially enacted in 1913 yet has done nothing to reduce the plant’s availability or use, is worth keeping.

Much of the public disagrees; that is why the voters this November will decide on an alternative. Proposition 19 would allow adults 21 years and older to privately possess and cultivate small quantities of marijuana for personal use. (Consuming marijuana in public would remain subject to punishment.) It would also permit local governments to regulate the retail sale and commercial cultivation of cannabis for adults.

Proposition 19’s proponents maintain that the enactment of sensible regulations and age restrictions regarding marijuana’s production, distribution and consumption will limit youth access to pot and better protect public safety. Feinstein disagrees, calling the measure “a jumbled legal nightmare that will make our highways, our workplaces and our communities less safe.”

Let’s assess her argument point by point. First, Proposition 19 explicitly states that it will not amend or undermine existing state law criminalizing motorists who operate a vehicle while impaired by pot. Driving under the influence of marijuana is already illegal in California, and violators are vigorously prosecuted. This fact will not change under the initiative.

Second, Proposition 19 in no way undermines federal drug-free workplace rules, just as the state’s 14-year experience with legalized medical marijuana has not done so. Further, it does not limit the ability of employers to sanction or fire employees who show up to work under the influence of pot. Just as a private or public employer today may dismiss workers for being impaired by legal alcohol, employers in the future will continue to be able to fire employees who arrive to work under the influence of marijuana.

Third, Proposition 19 seeks to enhance the safety of California’s communities by removing the commercial cultivation and distribution of marijuana from criminal entrepreneurs and moving it into the hands of licensed, regulated business people.

Proposition 19 would also allow local governments to reallocate law enforcement resources toward more serious crimes. Presently in California, more than 60,000 people annually are arrested for minor marijuana possession offenses. Proposition 19 would eliminate many of these needless arrests. The measure’s approval would unburden the courts, save millions in taxpayer dollars and allow police to spend their time targeting more serious criminal activity.

Marijuana is not a harmless substance, but this fact is precisely why its commercial distribution ought to be legal and regulated in a manner similar to the licensed distribution of alcohol and cigarettes, two legal substances that cause far greater harm to the individual user and to society as a whole than cannabis ever could. Society doesn’t tax and regulate alcohol because it’s innocuous; it does so because we recognize that it temporarily alters mood and behavior and thus should be regulated accordingly. There’s no reason why this same principle ought not to apply to cannabis.

It is time to bring long-overdue oversight to a market that is presently unregulated, untaxed, uncontrolled and monopolized by criminal entrepreneurs. It is time to replace nearly 100 years of failed marijuana prohibition with a policy of sensible cannabis regulation.

Paul Armentano is the deputy director of NORML, the National Organization for the Reform of Marijuana Laws. He is the coauthor of the book, “Marijuana Is Safer: So Why Are We Driving People to Drink?” (Chelsea Green, 2009).