But a recent Cato Institute analysis found that none of those nightmare scenarios have come to pass so far. Teen use is down, crime is flat and many other social and economic indicators are unchanged.
"The absence of significant adverse consequences is especially striking given the sometimes dire predictions made by legalization opponents," the Cato authors conclude.
The Public Policy Polling survey, commissioned by the pro-legalization Marijuana Policy Project, suggests that that's how many Colorado residents see it, too. About 61 percent of voters there say legalization has had a positive impact on the economy, and 58 percent say the tax revenue generated by legal marijuana sales has been good for the state.
Most interesting, from a public health standpoint, is the finding that nearly one in four Colorado voters say they know someone who is drinking less alcohol now that marijuana is legal. Research has generally shown that marijuana consumption is associated with fewer health risks — both to consumers and society as a whole — than alcohol consumption. If Coloradans are substituting marijuana for alcohol, the state could see some subtle gains in public health as a result of that shift.
There are, of course, negative outcomes associated with legalization, too. The Colorado Department of Health says marijuana-related emergency room visits are up. The state has also had some difficulty regulating edible marijuana products, such as candy and cookies, which have sent a number of kids to the hospital.
The survey found that men (55 percent) hold significantly more positive views on legalization than women (40 percent) do, and that Democrats (58 percent) and Independents (52 percent) are considerably more likely than Republicans (32 percent) to say that legalization has been good for Colorado.
But the biggest marijuana divide is seen in age: Three-quarters of 18- to 29-year-olds say that legalization has been good for the state, compared with 27 percent of voters over 65 who say the same.
Despite these divisions, however, a majority of Colorado voters (51 percent) would oppose any plan to repeal marijuana legalization. Only 36 percent would support such a measure.
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