'You are what you eat' notwithstanding, it is only recently that most consumers have become interested in the technical details of their food's composition, production and transport. With obesity and climate change now major concerns, and 'localvore' and 'food miles' entering the lexicon, shoppers are clamouring for information. And many food companies are happy to supply it, resulting in a dizzying array of multicoloured labels and claims.

But not everyone is happy. A proposed law in Indiana is the latest attempt in the United States to ban milk labels proclaiming that the cows from whence the milk came were not treated with recombinant bovine growth hormone (rBGH, also called recombinant bovine somatotropin or rbST). This hormone is produced by engineered bacteria, is virtually identical to the cow's own and can increase milk production by 10–15%.

There are two bad arguments for banning such labels. The first — that it is impossible to determine from the milk whether the cow was injected with rBGH — is the reason cited in the bill language. The second — that a proliferation of 'no rBGH' labels will train consumers to distrust the product — is the real motivation.

The first argument can be disposed of easily: it is already illegal to make false claims about a product. The second argument may seem more convincing. There is no firm scientific evidence that injecting cows with rBGH affects human health in any way, but prevalent labelling touting the absence of rBGH would suggest to consumers that there are some differences. The mandating of an additional phrase such as that agreed last month in Pennsylvania — “No significant difference has been shown between milk derived from rbST-treated and non-rbST-treated cows” — ameliorates this problem.

The hormone injections may not affect the milk, but they are rough on the cows: producing all that milk causes problems such as udder infections and lameness. For some consumers, this may be a sufficient reason to avoid milk from dairies using the injections. Indeed, it was, in part, animal welfare that led Canada and the European Union to ban them.

There are good reasons not to ban accurate labels. More information means that consumers can be more discerning, and not just about their own health. They can vote with their purchases for farming practices they prefer. And if a company wants to use a technology with a bad reputation, it is the firm's responsibility to educate the consumer about why it is beneficial. If consumers choose irrationally to reject it, that is their prerogative. Capitalism thrives on the irrationality of consumers, from their noted fear of smelling bad, to their preference for redness in apples, farmed salmon and fast-food signage.

Indeed, if consumers were suddenly to become rational, an economic cataclysm would result, as households in all the rich nations would cut their consumption to only what they really needed. Such a crash would no doubt make the current economic doldrums look like the mildest hiccup.