There might be an interesting evolution of "American opinion" unfolding:
While California's marijuana ballot initiative is garnering a lot of attention this election cycle, Gallup finds that nationally, a new high of 46% of Americans are in favor of legalizing use of the drug, and a new low of 50% are opposed. The increase in support this year from 44% in 2009 is not statistically significant, but is a continuation of the upward trend seen since 2000.
And there's an article in the current Newsweek about the increasing number of Republicans sneaking up on the idea of legalization:
As the ideals of the Tea Party's most vocal libertarians infiltrate the Republican ranks, and state and federal officials slash budgets even as they pump cash into an expensive war on drugs, some conservatives are making the case for legalizing marijuana.
[. . .]
Republican power broker Grover Norquist, president of Americans for Tax Reform, points out that legalization can make sense from a conservative perspective because it touches on issues of national security and fiscal prudence. “First, there is the mess that is Mexico. Narcoterrorism is made possible by our drug prohibition in the U.S. Then there is the cost of incarceration,” he says. Gary Johnson, the Republican former governor of New Mexico and a putative presidential candidate for 2012, says he believes that “Proposition 19 has the opportunity to be the domino that could bring about rational drug policy nationwide.”
Don't know about a "rational drug policy nationwide" anytime soon, but maybe we can at least have a more rational (i.e. less hysterical) debate about the issue.