The greatest fear among all the countries involved, however, is about the kind of Syria that will finally emerge from the conflict.
We must be wary of rose-tinted narratives about the past: sectarian tensions have been present, even if non-confrontational, in peaceful times.
If Assad is removed, who will succeed him? Even if there is a viable successor, it is likely that the bloodshed will continue, with infighting between rebel groups and lots of scoresettling.
Labour, the Lib Dems, two-thirds of Tory MPs and, now, Boris Johnson are all opposed to arming the rebels. This is an argument Cameron cannot win.
Adding weapons to a civil war will only exacerbate Syria's suffering. The UK must not follow the American lead.
The decision by the Obama administration to provide lethal aid means that the Prime Minister can no longer remain on the fence.
It is now the responsibility of the left to support the Syrian people, but be critical friends, remaining true to their principles.
We shouldn't allow the experience of Iraq to prejudice us against intervention in every other case.
Fleeing Syria does not always protect women from sexual violence.