A MAJORITY of Americans now favour the legalisation of marijuana. Two decades ago, 80% opposed it. Remarkably, about a third of the swing in public opinion came in just the past three years. It seems the tide has turned. However, William Galston and E.J. Dionne, scholars at the Brookings Institution, warn legalisers not to get too excited. "Support for legalization, though growing markedly", they write, "is not as intense as opposition, and is likely to remain relatively shallow so long as marijuana itself is not seen as a positive good." The trend in favour of legal weed, they observe, is not as inexorable as the trend toward the legal recognition of same-sex marriages. Much of the support for legalisation comes from the increasingly widespread belief that the benefits of prohibition have not outweighed the costs. Such pragmatism may be enough to shift opinions about the wisdom of legalisation, but it rarely generates the moral passion necessary to overwhelm fervent moral opposition and bring about lasting change. From a certain, rarefied liberal perspective (eg, mine), marijuana prohibition violates the individual's right to do whatever he likes with his own body as long as it does no harm to others, and is clearly unjust. The very existence of "victimless crimes" is enough to work me into a lather. Similar views about the injustice of paternalism drive most legalisation activists. Still, this sort of libertarian sensibility is not widespread. So why are views on marijuana changing? Because plenty of consequences of prohibition pique typical Americans.

It's monstrous to deny therapeutic marijuana to AIDS or cancer patients struggling with nausea, or to those who suffer from debilitating chronic pain. And it's fairly easy to engage sympathy and elicit indignation over this sort of cruelty. Drug warriors have often complained that the push to legalise marijuana for medical purposes is largely a pretext for full-blown legalisation, and they're right. Successful legalisation of recreational marijuana in Washington and Colorado came after the drug had become normalised through the medical-marijuana dispensary system. This is no happy accident. I've known a good number of legalisation activists who have fought hard and nobly to increase access to therapeutic marijuana. That they were also healthy, hearty enthusiasts of the drug's recreational uses is not incidental.

Medical marijuana has taken the legalisation movement far, but it may not be enough to tilt the whole country toward legalisation, as Messrs Galston and Dionne seem to suggest. But I'm not sure this means, as they argue, that support for legalisation is "likely to remain relatively shallow so long as marijuana itself is not seen as a positive good". There are other real injustices on which to hitch the cause, and legalisers are already hard at work. Racism is the new medical marijuana.

A new ACLU report, "The War on Marijuana in Black and White", exposes the outrageous inequities in the enforcement of marijuana posession laws. These two graphs make the case.

Note that marijuana use among young whites is slightly higher than among young blacks.