Thomas Wells teaches ethics and the philosophy of social science at the Institute for Philosophy at Leiden University, and at the University of Witten/Herdecke.

Like cigarettes, meat and dairy packaging should include no nonsense factual warnings about the negative consequences of one's consumption choices.

Just as with cigarettes, exercising our sovereign right to free choice requires that we be adequately informed about the significant negative implications of our choices by someone other than the manufacturer that wants us to buy their product.

In this case, the significant consequences relate to living up to one's ethical values rather than safe-guarding one's prudential interests in long-term health.

But the principle is the same.

Ethical warning labels would inform consumers of the physical and mental suffering involved in producing the animal products they are considering buying.

I envisage labels like this: "This chicken's beak was cut off, causing it intense pain until its death." And: "This cow's calves were taken away and killed to keep it producing milk."

Servers of cooked animal products, from lowly hot-dog stands to the fanciest restaurants, would also have to include these ethical warnings prominently on their menus.

Like cigarette packaging in some countries, the ethical warnings might include full colour pictures of the living conditions of the animals your food comes from. The labels could be graded to reflect the conditions under which the source animals lived and died - for example, if they pass the requirements of the various animal welfare certification programmes. That would allow better but more expensive standards of animal welfare to be recognised and encouraged by consumers.

Many restaurants might prefer to pay more for their groceries merely to avoid having pictures of debeaked hens ruining the aesthetic of their menus.

Still there are limits to how positive such labels may get. Even an animal that lives quite well and is killed quite painlessly has still had its life treated as a commodity, and this should be acknowledged. For example: "This chicken was killed at 7 weeks of age. It could have lived up to 7 years."

My proposal may seem outrageous and paternalistic on first reading. But it seems to me that such ethical warning labels are not only permissible in a free society; they are actually required by the liberal conception of freedom.

The conditions of "free choice"

A liberal society is defined by its respect for individuals' free choices in their private personal domain. First, whatever is not illegal is permitted. Second, making some practice illegal in the first place requires a public justification for its necessity and legitimacy that even those affected can appreciate.

John Stuart Mill's "harm principle" provides an ideal benchmark for this. It is legitimate to ban behaviour that harms others and their freedom to live their own life, but it is illegitimate to ban behaviour that merely offends others - even if they are the "moral majority" - by going against their private moral beliefs. Thus, in a liberal society, people are free to decide for themselves whether to do things that others strongly disapprove of, such as following "weird" religions, or engaging in unorthodox sexual practices, or eating meat.

Ethical warning labels would need to be mandated by law. But they would not restrict people's freedom of choice because consumers would remain as free as before to buy those products. Indeed, they respect the "democratic" mainstream view of meat-eating as a private ethical concern about which individuals should make up their own minds, on the model of a consumer lifestyle choice.

Of course, ethical labelling would interfere with the freedom of manufacturers to present their products as they wish, and would therefore need to pass a public justification relating to that. But this is not a great challenge. Corporations are not persons, and so their freedom of expression does not deserve intrinsic respect and can be abridged on purely utilitarian grounds. Labelling laws are consistent with the liberal understanding of individual rights and hence permissible in a liberal society.

Indeed, most countries already have labelling laws compelling manufacturers to present certain kinds of information (like use by dates) in a clear way, and these are often justified by customers' interest in having easily comparable information available in their decision-making (like information about nutritional values on packaged food and restaurant menus).

Nor need such labelling laws relate to scientifically proven "medical" facts, as the campaign for GM labelling demonstrates. Nor need they only reflect the interests of the majority of the population, as warnings that products may contain nuts demonstrate. Justifying an ethical labelling law merely requires showing that it could significantly help people to make better decisions.

This brings me to why I think ethical labelling is actually required by liberalism. The idea that the free choices of sovereign individuals are trumps contains a complication. What counts as a free choice? One can't tell merely from the fact that someone chose X over Y (an outcome) that their choice was a free one (a procedural quality). Let us leave aside the "free will" challenge and adopt the liberal starting point that individuals are indeed more or less sovereign agents who are responsible for their moral character and can therefore make choices for themselves.

Nonetheless, there remains a question mark over whether particular choices that we make are really free in the sense of being our own. In particular, if we are not sufficiently informed about both the negative and positive implications of the options we are presented with, we won't be able to relate those options to our own values and interests. We can still perform acts of choosing in such cases - we still have the power of choice. But we would not be choosing freely because we would not be able to exercise our right to choose in a way that follows from the personal moral beliefs that make us, us.

This issue seems particularly problematic in consumer choice cases where two factors are present:

Where the negative consequences of consuming something seem very significant and thus have a prima facie call on the attention of the chooser;

where the manufacturer of a product has a strong interest in encouraging its consumption even at the expense of the customer's own interests, and has substantial power to misrepresent the product to the consumer in a way that undermines their ability to consider its negative consequences.

These factors were clearly present in the case of cigarettes, a poisonous product designed to be addictive and routinely advertised in a deceptive way. I believe they are also present in the case of animal products.

The problem of moral irrationality

Killing or hurting animals is increasingly alien to our modern values and sensibilities. We don't gather anymore in the public square to enjoy the entertainment of cats being set on fire. Indeed, pets and working animals enjoy a variety of legal protections against mistreatment or even mere neglect that would have seemed astonishing 150 years ago. News items about incidents of animal cruelty, like dogfighting rings, generate widespread public outrage and disgust. Animal welfare seems to matter a great deal to many of us.

Yet, while the strength of this social consensus against inflicting suffering on animals is a fact, it is also a fact that a great many of us continue to consume meat and dairy produced by an industrial factory system that, in the name of efficiency, inflicts far more suffering on each individual animal than 150 years ago.

There are two possible solutions to this puzzle. First, that we just hold inconsistent moral views - that is, the majority of us have freely decided that some animals in some domains deserve special protections (the ones in our homes, and public spaces like zoos), and also that "food animals" don't. The animal rights movement has tended to focus on this moral inconsistency as a problem of moral irrationality. Thus, moral philosophers like Peter Singer argue that meat-eaters should modify their moral views and beliefs by affirming the moral status of animal welfare in all domains.

The second alternative is that something external to ourselves may be preventing us from acting consistently by applying the strong moral views we have developed about the treatment of animals to the animal products industry. In this perspective, the problem is not that our moral reasoning has gone awry, but that our freedom to make ethical choices of our own has been infringed. This consumer sovereignty perspective is the basis for my proposal for ethical labelling.

The animal products industry has adapted to society's changing moral views about animals as well as to the technological possibilities of factory farming. Noting that most of us cannot bear to see animals suffer, they have endeavoured to seclude livestock and their slaughter from our gaze. When we go to a supermarket or restaurant we are presented with meat rather than with animals, and with deliciousness rather than with killing.

This is an obviously one-sided and deliberately deceptive presentation of the basic ethical facts about animal products that have a prima facie call on our attention. It undermines our ability to choose what we eat in a way that is consistent with our moral beliefs about the treatment of animals.

Ethical warning labels would allow people to make better informed and therefore freer choices by breaking open the controlled and biased information environment created by the animal products industry.

Response to objections

Some will argue that ethical labels would be coercive and thus undermine free choice. There are at least two routes to this conclusion which I will consider in turn.

First, the idea that such labels are designed to be emotionally manipulative and this actually undermines people's ability to make a rational choice. The problem with this critique is that emotions are an indispensable part of our moral reasoning. Indeed, the core ethical argument against eating animals developed by the modern animal rights movement associated with Peter Singer is that animal suffering is of the same kind as human suffering. His argument is a call for empathy across the artificial boundaries which restrict us from imagining and taking seriously the suffering of others. This is rather different from mere sentimentalism. It seems to me that truthful ethical warning labels merely suggest that act of imagination rather than enforce it.

In addition, one must acknowledge that the emotional manipulation argument goes both ways. Advertisers and restaurants produce sophisticated "food porn" that artificially inflates our lust for meat, and manufacturers tweak recipes to manipulate our sense of the deliciousness of animal products. If their emotional manipulation is permissible, surely turn about is fair play.

Most people by now have some understanding of the fact that the way livestock animals are kept is rather horrible, but in the moment when we make our consumption decisions this rather abstract knowledge must go head to head with the full sensory propaganda of companies that are only interested in making us buy as much of their products as possible. Just as with cigarettes, there is a strong case for presenting the negative side of the case at the moment of purchase just as forcefully as the positive case is now presented.

Second, it may be argued that there is an inconsistency between the public justification for such labelling laws (enhancing freedom of choice) and the motivations of those who would support them (to induce people to reduce their consumption of animal products).

The model here might be the introduction in some American states of laws requiring that women seeking an abortion first watch an ultrasound of their foetus. The Republican legislators behind these laws give a public justification for this kind of law in terms of supporting women's freedom of choice, but their actual motivations are, rather obviously, to reduce the number of abortions women have, in line with their private religiously based moral views that abortion is killing if not murder.

Likewise, although ethical labelling laws can be given a superficial justification in terms of free choice, they are really about a minority group (animal rights fundamentalists) seeking to impose their own moral views onto society as a whole in an indirect and illegitimate way.

This kind of partisanship is disappointing. Democracy should aspire to more than the kind of tribalism that rejects proposals merely because they come from the wrong party. Proper public reasoning requires focusing on the quality of the public justification for policies like ethical warning laws rather than ad hominem suspicion of the motives of people that support them. Objectors must show one of three things: that the concept of ethical labelling is inconsistent with a free choice model (principle clash); or else that it is likely to undermine it in the longer term (bad consequences); or else that, as in the case of abortion perhaps, the free choice model is itself inadequate (wrong theory).

Yes, the consequence of mandating ethical warning labels on animal products would likely be a dramatic reduction in their consumption, and this is certainly what many supporters of such a law would like to see. But this no more counts as evidence of coercion than the fact that a university education correlates with liberal political views and lower religiosity proves that universities are a conspiracy against the Republican Party.

Evidence that people change their minds is not necessarily evidence that their minds have been changed for them. Indeed, supporters of ethical warnings can fairly claim that they do not impose contentious moral views on other people, but only help people to better live up to their own existing moral views if they wish to do so.

Many meat eaters justify their lifestyle by reference to their ability and right to make their own free choices. But if they are already making a free and fully informed choice that follows from an ethical value system which rates the moral status of animals simply as "delicious," then it hardly seems that providing factual information about the suffering of livestock animals could affect their consumption behaviour. (Here they resemble smokers who genuinely don't care about living past 70.) Because these meat eaters are already choosing freely - according to their personal moral beliefs - labelling laws could not affect them.

Those meat eaters who would be affected by labels would be those who already suspect that their practice is morally wrong for them - that is, inconsistent with their own personal moral beliefs about how animals should be treated - but prefer to evade being confronted with that fact or find it hard to resist temptation in the moment of decision. (Here they resemble smokers who don't want to acknowledge that tobacco causes cancer.)

Ethical warning labels provide information at the right time and place to help such people live up to their own moral beliefs, but do not force them to. The burden of proof is on objectors to explain why this should be seen as suppressing rather than as supporting their freedom of choice.

Thomas Wells teaches ethics and the philosophy of social science at the Institute for Philosophy at Leiden University, and at the University of Witten/Herdecke. He blogs at The Philosopher's Beard.