Call me soft, but I can’t be blase about mass murder. The genocide carried out by the communists in Cambodia in the 1970s, the slaughters of Tutsis by Hutus in Rwanda in 1994, of Muslims by Serbs in Srebrenica in 1995, of Darfurians by Sudanese jihadis in recent years — these were shocking, appalling atrocities by any standard. They also were failures of American and European leadership, proof that the “international community” is a fiction and that the U.N. is useless.

So when President Barack Obama justified the intervention in Libya based on fear of a “bloodbath” — following Moammar Gadhafi’s vow to show “no mercy” to rebels in the country’s east — I was supportive. “We knew that if we waited one more day, Benghazi, a city nearly the size of Charlotte [N.C.], could suffer a massacre that would have reverberated across the region and stained the conscience of the world,” Obama said.

Across the Mediterranean, many Syrian opponents of Bashar al-Assad took that to mean there was a red line the dictator would not be permitted to cross. Other Syrians argued that Obama was not sincere; that his concern for Libya derived from Europe’s thirst for oil and distaste for North African refugees. As the Syrian death toll has mounted — estimates are now near 19,000 — this interpretation has become difficult to dispute.

Western reluctance to take steps to stop Assad’s butchery created a vacuum al-Qaida has been attempting to fill. When the U.S. was in Iraq, Assad facilitated the flow of foreign jihadi killers across his eastern border. Now the jihadis are coming home to roost, with three of Assad’s top deputies killed by a bomb on July 18.

In that, there is rough justice but not irony: The jihadis seek domination in Iraq (where al-Qaida attacks have been rising sharply since the U.S. withdrawal), Syria, Yemen, Afghanistan, Pakistan, Somalia, Mali — whatever lands they can get their bloody hands on. They will accept help from anyone who will give it. But Islamists, like Communists, are not burdened by such bourgeois sentiments as gratitude. That should have been among the key lessons we learned after helping the mujahedeen end the Soviet occupation of Afghanistan.

Assad’s killing machine has been weakened and may be defeated. I can’t predict when. What can be foreseen is that the day Assad falls, there will be an explosion of anger not just against him and those in his inner circle, but against all Alawites, his minority sect (about 12 percent of the population), and against those Christians who long ago decided that an alliance with Assad was their least-worst option. The jihadis will take the lead in this butchery, and make every effort to remain leaders thereafter. What will be the American and European response?

Former CIA analyst Bruce Riedel is among those arguing that “one of the priorities of the international community after Assad falls will be to protect the Alawite community and its allies from vengeance.” Color me dubious. After failing to take serious steps to protect Assad’s victims, we’re going to make it a “priority” to prevent revenge against those viewed as Assad’s accomplices?

On the other hand, I can’t go as far as my colleague Lee Smith, who wrote: “The idea that the Assad regime and its supporters warrant American protection simply because they are a minority group is not only strategically incoherent but immoral ... Does anyone believe that in the aftermath of World War II it was the role of the United States to save the Nazis and their allies from the Red Army? Of course not.”

American forces in Europe did indeed turn a blind eye not only to Soviet brutality but also as the French roughly settled scores with fellow citizens who had been cozy with German invaders. But that was then, this is now, and I’m not sure the same rules apply. And there is this to consider: What would follow the slaughter of Syrian Alawites and Christians? What kind of Syria could be built on this graveyard?

Such concerns have policy implications. To stop Assad’s carnage as soon as possible requires providing material support to Syrian rebels, very carefully and probably covertly. We want our Syrian friends — and we do have some — in possession of more money and guns. That will not only help them defend themselves against Assad’s troops now, it also will enhance their strength against other factions later. What’s more, Obama has said many times that we are at war with al-Qaida. Surely that implies we not permit al-Qaida to get the upper hand, not in Syria, not in Iraq, not in Africa, not anywhere.

When the fighting is over, the last thing we should want to see is the rise of yet another strongman. A regime dominated by the Muslim Brotherhood would be no victory for freedom either.

Other outcomes can be imagined. Syria is a mosaic of ethno-religious communities. Good fences will be required to make them good neighbors. Start with Syria’s Kurds who have been aloof from the fighting, relatively safe in their northeastern territories. In a post-Assad Syria, they’ll want substantial autonomy. They should have it within a federal Syria that guarantees minority rights to Alawites, Christians, Druze and other groups. Al-Qaida won´t like it, Iran and Hezbollah won´t like it, and some in the Sunni majority won’t like it either. But those who hope to rebuild Syria as a decent country, independent and at peace within its borders, should readily grasp the benefits.