Stay out of it. Syria is of little value to the west, so at a selfish level there's no justification.
And then who do we support? The government thugs? The resistance army thugs? The Islamic revolutionary thugs from Jordan who are starting to stick their oar in militarily? All the groups are guilty of reprehensible behaviour, all have war criminals among them. Whichever of these 3 groups prevail will bring anew and dark chapter to the history of this country.
And what's the moral mandate? Would we have been happy if Syria had started on us because we put troops on the streets of Ulster to quell revolutionary activity?
There is no strategic, moral, military, economic reason to stick our nose in, and those with even short memories must surely be able to see what a cluster f**k Libya turns out to be.
Leave it, let them get on with it. If we're going to stick noses into every tin pot banana republic that's unpleasant the need have been in Zimbabwe 3 decades ago, or even supported the Smith government when it declared UDI. If we're going to start butting in to countries just because the leader is a toaster then there's a long list of much more worthy targets in the queue ahead of Syria.