The evidence that the Palestinians in the West Bank and Gaza live under intolerable conditions, which deserve some comparisons to the conditions suffered by people under colonial overlords or under the South African apartheid system, is overwhelming. The restrictions on free movement and on economic activity; the inequitable distribution of land and water; the extent of the illegal encroachment by Jewish settlers - all these shock even those who travel to the area with open minds. It is also true that the Israeli army, faced with an uprising of stone-throwing Palestinians, uses bullets when other armies, such as the British in Ulster, might use CS gas.
But does this justify the use of terror, of the sort that took at least 16 lives in a suicide bombing attack in Israel on 6 June? Can India's occupation of Muslim Kashmir, and its failure to hold a plebiscite that the UN demanded more than 50 years ago, justify terror attacks on India by Islamic militants? Can the general poverty, misery and humiliation of the Arab world be used to justify the atrocities of 11 September? To Michael Ignatieff, writing in the latest issue of Index on Censorship, the answer is simple. Terrorism is an evil. "Why? Because it seeks to frighten human beings, rather than persuade them; because it replaces the ballot box with the bullet; because it provokes terror in return; because . . . violence is the enemy of rational politics and rational politics is the only hope we have to create justice and peace. The . . . sin of terrorism is not just that it kills and maims innocent human beings: it corrupts faith in the possibility of rational, ie, peaceful political change."
Mr Ignatieff dismisses the suggestion that one man's terrorist is another's freedom fighter. A terrorist targets civilians, a freedom fighter confines himself to military targets. It is as simple as that. Likewise, Mr Ignatieff insists, a military response that hits civilians as "collateral damage" is not the same as one that hits civilians exclusively and deliberately. He thus concludes - from his perch at the Carr Center for Human Rights Policy at Harvard University - that, although we may argue about the details of how and where to prosecute it, a "war on terror" should leave us with no uncertainties: "It really is the case that you are either on one side or the other."
This argument looks admirable in principle and, to some extent, in practice. As Mr Ignatieff rightly reminds us, many of the greatest victories for freedom and self-determination over the past century were achieved largely without terrorism: the collapse of the Soviet empire, the end of British rule in India, civil rights in America. Even in Northern Ireland, the greatest advances in the lot of the Catholic minority were achieved by the civil rights movement, not by the IRA; and, in South Africa, too, terrorism had only a small role in the defeat of apartheid. Oppressive regimes collapse when they lose their own moral confidence. Terrorism achieves the opposite: it shores up the oppressors' sense that they are in the right and that their opponents are subhumans who deserve subjugation. This has patently been the case in Israel, where the peace movement becomes weaker with each suicide bombing. It has been the case, too, in the US, where even liberals such as Mr Ignatieff are ready to defend the American treatment of prisoners at Guantanamo Bay and where Christopher Hitchens (see Letters, page 36) turns on his former leftist comrades with the same scorn that he previously reserved for the rich and powerful.
If Mr Ignatieff is right, and we have to decide which side to take, all this may be helpful. But Europeans, who can afford greater distance, may question the argument. First, what is meant by "a war on terror"? One can deplore terrorist attacks on civilians - and cry for the dead of New York or Israel - without remotely condoning the response of either George Bush or Ariel Sharon. Fighting terrorism demands better intelligence and better security, which left-wing liberals tend to dislike. It also demands better control of international financial transactions, which right-wing liberals tend to dislike. (A task force set up by the G7 proposed new rules to tackle terrorist money-laundering; so far, not one leading country has implemented them.) Bombing countries that may or may not be harbouring terrorists, and overthrowing their governments, looks like a rather blunt instrument.
Second, a state army very easily slips into terror itself even as it claims that its efforts are directed against legitimate targets. The Israeli army insists that its assaults on Jenin are intended purely to root out terrorists: if civilians are killed, it is only because terrorists are apt to hide out in their homes and, in most cases, are being deliberately sheltered. It is here that Mr Ignatieff's principles begin to crumble. How do you define a military target? Does the Pentagon, with its hundreds of civilian employees, count? Do the Jewish settlers, occupying what the Palestinians regard as their land? If not, Palestinians must presumably confine their resistance to attacking Israeli military bases and armed patrols, and then take the punishment (which, on past form, will be no less fierce than the punishment for a suicide bombing) in their own homes. This hardly sounds like a fair and equal contest.
One can thus agree on the evil of terrorism and agree also that, more often than not, it is politically foolish. But there are gradations of terrorism, of grievance, and of despair. Faced with these complexities, we should resist peremptory calls, even from Harvard professors, to make up our minds. There is no obligation to take one side or the other, to join the mutually uncomprehending camps that make so many of the world's troubles so difficult to resolve.