One reason given for western passivity is that the US, in particular, has comparatively little leverage. Syria is already the subject of American sanctions and diplomatic relations are tenuous. More to the point, however, the US and Britain worry that Assad’s fall, and the prolonged instability, even civil war, that they assume would ensue, would undermine Israel-Palestine peace efforts (such as they are), upset delicate political balances in Lebanon and Iraq, and provide an opening for al-Qaida-style extremists.
Regional countries also favour the Syrian status quo for self-interested reasons. Turkey believes chaos in Syria could revive separatist agitation among the country’s Kurdish minority, with knock-on impact in south-east Turkey. Israel worries a new Syrian government might push more aggressively for the return of the Israeli-occupied Golan Heights. Saudi Arabia is opposed, in principle, to anything that smacks of democracy.
Nor is Europe exactly cheerleading change, despite the obvious contradiction in its attitude towards Muammar Gaddafi. The fact that the EU is Syria’s largest trading partner, and Europe buys Syrian oil, may have a bearing.