The death of the foreign correspondent Marie Colvin has two meanings. One is that journalism is about more than prurience and moral and financial corruption – contrary to the impression that might have been given by the events that led to the Leveson inquiry and by some of the practices that have been exposed since, and of which there may be worse to come this week. Journalism is also about the reporting of truths and injustices, and especially those that the powerful and the malign would rather were not reported.

The other meaning is in one of those truths, the humanitarian emergency in Syria, on which Colvin was reporting when she was killed. In her last words she said: "In Baba Amr. Sickening, cannot understand how the world can stand by and I should be hardened by now. Watched a baby die today. Shrapnel, doctors could do nothing. His little tummy just heaved and heaved until he stopped. Feeling helpless. As well as cold! Will keep trying to get out the information."

She wanted the world to know that Bashar Assad's forces were perpetrating terrible crimes upon their people. We have known that for a year now, but international action to do anything about it has been dismissed as unlikely because there is no consensus at the United Nations. In the great tradition of war reporting, Colvin sought to stir the conscience of the world by bearing witness to the human consequences of an unjust military campaign.

The Independent on Sunday hopes that she succeeds posthumously. This newspaper supports the doctrine of a "responsibility to protect", as adopted by the UN in 2005. We wish it had been acted on in Rwanda in 1994 and in Bosnia in 1995. We were glad that it was acted on in Kosovo in 1999 and in Libya last year. Of course, conditions must be met. Military action must either be authorised by the UN Security Council, or be to prevent the killing of large numbers of civilians. Both conditions were satisfied in imposing a no-fly zone over Libya last year, when Gaddafi threatened to take his revenge on the people of Benghazi.

Syria is different, as Paul Vallely explains today. Russia, supported by China, will veto any UN authorisation for intervention. Intervention would still be justified, however, on grounds of averting a worse humanitarian disaster. But it needs to be effective. A no-fly zone would not protect the people of Homs or the other towns that are rising up against the regime, because the Syrian military is using ground artillery to attack them. If there is one thing that even the most wide-eyed neo-conservative has learnt from Iraq, it is that the adverse consequences of a ground invasion are likely to far outweigh any good that might be done – even leaving aside the dangers of a proxy war against Russia or Iran.

Yet there are things that can be done. The European Union is going to tighten sanctions another symbolic notch tomorrow. More importantly, world opinion should be focused on the medical crisis in Homs. The International Committee of the Red Cross is working through the Syrian Arab Red Crescent to try to help the wounded, but under tight Syrian government restrictions.

The Independent on Sunday joins with our colleagues in the British media to demand safe Red Crescent access to Homs. In addition, we want the wounded journalists to be allowed out and the bodies of Marie Colvin and that of the French photographer Remi Ochlik to be returned. Perhaps even Assad and Vladimir Putin can be shamed into that.

Let Marie Colvin's legacy be twofold, then. First, a celebration of good journalism and a determination to defend it from the well-meaning attempts to use the Leveson hearings to encroach upon it. Second, a new determination to find the most effective way to mobilise the international community to protect the Syrian people from their appalling rulers.

Liberal interventionism is always evolving, always adapting itself to different situations, but the moral impulse behind it grows stronger all the time, despite, or even because of, the mistakes made by the US and the UK in Iraq. It is generally agreed that Bashar Assad's days in Damascus are numbered. We must hope that Marie Colvin's legacy will be a significant shortening of that dictator's time in power.