Boris Johnson, London’s mayor, distanced himself from his own Conservative Party leader on Sunday when he questioned the wisdom of arming Syria’s rebels.

While Prime Minister David Cameron has long called for increasing Western support of “moderate” opposition forces in Syria, Johnson, who might rival Cameron for the party leadership ahead of the next election, argued in The Telegraph newspaper that they cannot be kept separate from religious extremists who are fighting on the same side. “How are we meant to furnish machine guns and anti-tank weapons to one set of opposition forces, without them ending up in the hands of men like the Al Qaeda affiliated thugs?” he wondered.

The answer is that we have no means of preventing such a disaster, any more than we can control what kind of “government” the rebels — if they were successful — would form in Damascus.

The most effective elements in the armed opposition movement do appear to be radical Islamists whose aim, according to Johnson, is not freedom, rather “a terrifying Islamic state in which they would have the whip hand.”

Fearing such an outcome in a conflict that has divided world powers for more than two years, Western countries have limited themselves to providing “nonlethal” aid to the opposition, including communications and sanitation equipment as well as British body armor, while allied Arab Gulf states, including Saudi Arabia and Qatar, did supply weapons. China and Russia have opposed such intervention.

The United States announced last week that they, too, would start sending weapons into Syria, supposedly following conclusive evidence of chemical weapons use in the conflict although The Washington Post revealed that the decision to arm opposition forces was actually made weeks in advance.

Late last month, France and the United Kingdom prevented the European Union from extending its weapons embargo on Syria, enabling them to send whatever equipment they want to the rebels — while chastising Russia for doing the same in support of the other side.

British and French officials insist that the aim is not to join the war effort on the rebels’ side but only to put their capabilities on par with those of the loyalist forces. Leaders have also demanded that President Bashar Assad step down, though, to make way for a democratic transition.

Whatever the exact goal of providing weapons, Johnson sees no good way out of the crisis. “Surely to goodness it is time to recognize that no one can win this conflict because it has become at least partly a religious conflict, between Sunni and Shia.”

No one can win that conflict because it is almost beyond reason. It is an argument about the protocol that surrounded the succession of the Prophet Muhammad — in the seventh century AD! One side or the other might technically “win,” and impose a government over the whole country. But unless that government has the approval of both Sunnis and Shias, we are doomed to sectarian violence and reprisals forever.

Johnson has also sounded more Euroskeptic than the prime minister, suggesting that leaving the European Union would not be as “cataclysmic” for British jobs as supporters of membership claim although he does not advocate such an exit.

Cameron is under pressure from Euroskeptic lawmakers to call a referendum on Britain’s membership of the body before, instead of after, the next general election, scheduled for 2015.