The acute dilemmas facing Western governments over Syria illustrate how foreign policy can often be the art of the impossible. The essential problem is that Britain and her allies have two incompatible objectives: they want to hasten the downfall of President Assad, while also bringing the country’s bloodshed to an end. You can’t do both at the same time.
Accelerating the end of a regime as ruthless as Syria’s will inevitably entail more violence. If you choose this option, you are effectively placing Assad’s political demise ahead of the need for peace.
The case for the defence will be that removing the regime is the crucial precondition for restoring stability in Syria. Assad’s presence in office is the chief cause of the violence, so if you care about peace, he has to go. But there are two problems with this argument: 1) getting rid of Assad will probably involve a protracted and bloody struggle and 2) there is no guarantee that harmony will break out when he finally departs.