In short, a long intra-Islamic war left nobody safer, wealthier or wiser. Nor did it leave the West morally untainted. The U.S. embraced Saddam Hussein as a counterweight to Iran, and later tried to ply Iran with secret arms in exchange for the release of hostages. Patrolling the Strait of Hormuz, the USS Vincennes mistakenly shot down an Iranian jetliner over the Gulf, killing 290 civilians. Inaction only provides moral safe harbor when there’s no possibility of action.

Maybe that’s what President Obama is secretly aiming for. Had he armed Syria’s rebels early in the conflict, he could have empowered a moderate opposition, toppled the regime, sidelined Sunni jihadists, prevented the bloodbath we now have, stemmed the refugee crisis and dealt a sharp strategic setback to Iran—all without any U.S. military involvement.

Had he moved against Assad after the latter’s use of chemical weapons, the president could have demonstrated the seriousness of U.S. red lines—this time with limited and surgical use of U.S. military assets. (By the way, whatever happened to that U.N. fact-finding mission on Syrian chemical weapons that Mr. Obama promised back in April?)