When New Mexico's governor Bill Richardson, a plausible candidate for the Democratic presidential nomination, decided to ban cock-fighting this week, the press treated his decision as a "no-brainer". Although cock-fighting has deep roots in the historically Hispanic state, it is already illegal in a third of New Mexico's counties, not to mention all other US states except Louisiana. US federal law forbids transporting fighting birds across state lines. Two-thirds of New Mexicans favour a ban.

Yet Mr Richardson – a politician of refreshing forthrightness on such controversial issues as legalising marijuana for medical use (which he favours) – anguished over cock-fighting until recently. He has been lampooned, by comedians and columnists alike, for opining there are "strong arguments on both sides".

But Mr Richardson was right. In politics, no-brainers are seldom as obvious as people claim. They are often issues that, once you start thinking about them, prove more complicated than they seemed. There are indeed strong arguments for and against cock-fighting. On one hand, strapping honed metal talons on to birds and goading them to fight seems barbaric. On the other hand, they are only birds. The arguments Mr Richardson rejected have deeper roots in American tradition than the arguments he listened to.

The most straightforward argument for banning cock -fighting was made less often in New Mexico than one might expect. It is that cock-fighting is almost always associated with illegal gambling. Cock fights are one of the few US gambling venues not under the control of government or large companies. Those who condemned the practice – including the New Mexico-based Hollywood personalities Ali MacGraw and Pamela Anderson – did so on other grounds, those of animal rights. This is a coherent ideology, although in the cock-fighting debate it has seldom been presented in its most coherent form.

The bill's sponsor, state senator Mary Jane Garcia, said: "I'm against any kind of violence: violence against women, violence against children, violence against animals." Mixing up these kinds of violence blurs distinctions between, say, mugging old women and eating veal. If that is the bedrock position of the anti-cock-fighting movement, it does not command majority support.

Animal rights measures often win a marginal improvement in animal comfort at a high price in human freedom. The New Mexico Gamefowl Breeders Association said: "We place the rights of the people of New Mexico above the rights of a chicken." One local opponent of the ban told reporters: "You start doing away with cock-fighting, then you open the door and they're going to start doing away with rodeos."

Otherwise, this slippery-slope argument rarely came up. The idea of liberty – that New Mexicans ought to be free to arrange and attend cock fights if they wish – was not the focus of debate. Instead, pro-cock-fighting forces pleaded for their hobby on two grounds. First came economic utility. Tourists like cock-fighting, its defenders said, and it employs people. Second was the ethnic identity of the cock fighters. New Mexico, with its 16th-century mission churches and its non-"Anglo" majority, is heavily marked by Spanish-speaking culture. It is no coincidence that the two states in the continental US that permit cock-fighting are those least marked by Anglo-Saxon legal and political traditions. So one enthusiast told the Associated Press that, since the most ardent cock-fighters were Hispanic, opposition to their doing whatever they please "borders on being a racist issue". Cock-fighting was defended not as a citizen's right but as an ethnic privilege.

The anti-cock-fighting reformers never dismissed this principle as nonsense, as they very well could have. They simply denied, a bit absurdly, that there was any link between the sport and Spanish-American culture. "It's a gruesome, barbaric sport," said Ms Garcia, "and then they try to convince me it's a cultural sport. I don't think so." The controversy in New Mexico may even advance assertions of ethnic privilege. One possible outcome, according to the Gamefowl Breeders, is that the practice will be allowed to continue on Indian reservations, which have been granted monopolies on various industries that once fell under the heading of "vice".

It used to be, under the US system, that one could do anything that was not expressly forbidden. Now one is forbidden to do anything one cannot make an explicit case for. The burden of proof has shifted. This shift was clearest in criticisms that Martin Chávez, the mayor of Albuquerque and a key cock- fighting foe, made before an animal welfare conference last summer. "You can't be president of the United States," he said, "if you think cock- fighting is a good thing." In this view, Mr Richardson's refusal to ban cock-fighting would have been tantamount to an enthusiasm for it.

Cock-fighting is one of a range of cultural clashes in the west that pit a "mainstream" against a "subculture". These battles – over controversies that include foreign-language instruction in schools, gay marriage and mosque-building – have no particular ideological colouring, but they are debated in the same new way. Defenders of liberty are no longer pitted against defenders of order; instead, advocates of minority interests are pitted against advocates of public utility. Maybe the reason Mr Richardson was laughed at for saying there were good arguments on both sides is that he was thinking about the old values of liberty and order. These values require balancing, not the absolute victory of one side over the other. As such, they require more thought. Whatever one thinks of cock- fighting, it is dispiriting to see how weak an argument sufficed to overturn an old tradition and how tongue-tied the tradition's practitioners were in their own defence.

The writer is a senior editor at The Weekly Standard