This is not to deny either the sincerity or the seriousness of the demonstrators at Brightlingsea and Shoreham. How we should treat animals has been an unresolved problem since Darwin. The Old Testament showed clearly that God had put animals on earth for humanity's use. The acceptance of the theory that humans and monkeys had common ancestors - and the later discovery that men and chimpanzees had 98 per cent of their DNA in common - created a new set of moral questions. Yet only in the last 25 years have academic philosophers begun to take an interest.
They have raised hugely complex questions that go far beyond simple sentimentality about animals. Most people can accept that we should take care of animals because they help to enrich our natural surroundings and play an important ecological role. The difficult questions arise when we consider the extent to which we can justify inflicting pain on animals. Is the pleasure that some people get from eating white veal a sufficient reason for inducing anaemia in calves? Should animals be used for medical experiments that may develop treatments to relieve human pain and suffering? (If your answer is "no", should you refuse such treatments?) Most people draw the line somewhere - at torturing a domestic cat, for example. But the scope for argument is endless.Does the suffering of a pig, said to be the most intelligent farmyard animal, matter more than the suffering of a chicken or, for that matter, a herring? If so, what about a subnormal pig? The answers are based more on sensibility than on logic.
This is why hard questions need to be asked about the motives of demonstrators at Shoreham and Brightlingsea. First, those who are so concerned for animals seem careless of their fellow human beings. Obstructing roads is not usually the right way to achieve change in a democracy. The animal rights movement has achieved remarkable advances through persuasion and lobbying: vegetarianism is flourishing, the use of animals for fur and cosmestics is widely frowned upon. It can achieve most of its aims by convincing consumers: to persuade them not to buy meat or to visit circuses, for example. But peaceful pickets outside supermarkets are unglamorous.
The second question must be about the demonstrators' priorities. Political issues, at home and abroad, may not be as clear-cut as they once were but human beings still suffer poverty, injustice, wrongful imprisonment, torture. Demanding an end to "speciesism" is all very well but there is still enough racism in the world to preoccupy the caring and compassionate.
That leads to the third question. What kind of compassion is this? There have always been people, mostly clever and mostly middle class, who like to believe that they have the answers for injustices suffered by others. The trouble is that human beings are apt to answer back: they don't want this kind of charity, they don't like that political programme. The urban proletariat has been a particular disappointment, embracing capitalist values given half an opportunity. Now, the proletariat is in decline and the ideology that was supposed to liberate it is all but dead. Animal liberation is the ideal replacement: victims that can never speak for themselves, injustices so numerous that they can never be wholly righted, prejudice and discrimination that can never be entirely eradicated, an "ism" for all eternity.