“No one can here understand how the international community can let this happen.” So said Marie Colvin, in an interview given from Homs, just a day before she herself was killed by a Syrian bombardment.

Colvin, a gallant war reporter, put her finger on a recurring dilemma in international politics. Does the outside world have a duty to intervene to prevent the mass killing of civilians?

Those who see vicious cruelty up close tend to react like Colvin. Almost all the journalists I know who covered the Bosnian war became convinced advocates of outside intervention. It is the natural human response. You see innocent people being killed, day after day. You know that there is a vast arsenal of military might, sitting back home, that could overwhelm the aggressors. It seems impossible and immoral not to advocate stopping the killing. I had a similar reaction after being appalled by a visit to East Timor, when it was under Indonesian occupation.