However, the terms of the debate are confused. The very phrase "animal rights" means different things in different mouths. Some take a denial of animal rights to be a licence to do what we like to animals. Others would say that if animals have rights, it is practically never legitimate to harm them. Talk of rights contributes to the slide into extremism.

It would be much better to stop talking about rights and instead to ask two simple questions. When, if ever, may we make animals suffer? And when, if ever, may we kill them? Extremists prefer the simplest possible answers: either "always" or "never". But it is obvious that we can instead opt for a moderate view that rejects harming animals except when the benefits to them and us are sufficiently great. We may also need to treat species differently. The more sophisticated an animal's mind, the more it is deprived by a premature death. Typically, it may be worse to kill a gorilla than a chicken; but it may well be worse to kill a human being than either.

To change the terms of the debate is one thing; to raise its tone is quite another. Too many people hold strong views about animal welfare, uncontaminated by any commitment to consistency, argument or evidence. They think they know how much an animal suffers because they can imagine what it is like to be that creature: they know how much they'd hate to be chased by a pack of hounds, and surely the fox must feel the same way. This is the crudest kind of anthropomorphism. Just as we can't tell what an animal likes to eat by the power of pure imagination, so we can't always tell what causes them distress. We need scientists who study the physiology and behaviour of animals to help us find the truth.

By threatening the scientists who carry out such research, animal welfare protesters are crippling their own campaign. Of course this research must be carried out responsibly. But there can be no progress on animal welfare reform without the understanding of animals and their needs and interests, which only science can provide.

Too many people's views on animals are distorted by massive blind spots, not least a wilful reluctance to confront animal suffering when it contributes to their own interests. While hours of parliamentary time were taken up with concern for the few thousand foxes killed in the hunt, few raised any worries about where our food comes from. But if you look behind the plastic-wrapped drumsticks on our supermarket shelves you find the most urgent animal welfare issue that we face.

Millions of chickens are kept in tiny cages, fattened so quickly that their bones break under their own weight, suffering from salmonella and other diseases. Hundreds of thousands of birds are held in vast sheds, never breathing fresh air before they are slaughtered. Turkeys, pigs and dairy cattle are kept in similarly poor conditions.

Factory farming involves millions more animals than foxhunting, and the prolonged ordeal of a broiler chicken probably causes more harm to each creature, too. Most people who tuck in to their Sunday roast do not take pleasure in the suffering of their factory-farmed food; in fact, they put such thoughts as far away as possible. Hunters, by contrast, may enjoy the kill and chase. But this on its own does not justify the focus on hunting. Anyone concerned for animal welfare should put the reform of farming right at the top of their priorities. We should no longer support factory farms by buying the food they produce.

We like to think that our treatment of animals shows us at our most civilised and compassionate. In reality, it shows us at our most squeamish. We don't like to see animals suffering in front of us, but are quite prepared to turn a blind eye to whatever goes on behind the factory doors.

Another mark of civilisation is a willingness to go beyond the bounds of our selfish desires to think more widely about our place in the universe. May we exploit the resources of the natural world until they are utterly destroyed? Are there ethical limits to our dominion? The very fact that we can pose such questions distinguishes us from other animals. But the most basic foundations of a civilised debate about them - a respect for reason, argument and the other's point of view - are in short supply. We have a responsibility to do better in the future.

· Alison Hills is a lecturer in philosophy at the University of Bristol. Her book Do Animals Have Rights? is published by Icon

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