I think it's a good idea to demand of states, including the UK and USA, that they give the Syrian rebels with sufficient armament to get rid of Assad and his régime.
Most people won't understand why if you want the rebels armed and the West is best placed to do it, why you wouldn't want the West to do so, but having read for example, William Blum's* account of the many, many countries the CIA have turned over I can appreciate the reluctance, but I don't think Syrians have the luxury of waiting for a more kind-hearted arms supplier. I wish they could make or take all the weapons they need, but if wishes were horses, then beggars would ride.
I think many of the specific arguments are misplaced. Arguments that we don't know who the rebels are/the weapons will fall into the wrong hands/they will promote instability are either generally wrong, will have the opposite effect from that intended, or are exaggerated (not necessarily in that order).
The idea that America is always going to be a bad thing, is similar to the one socialists often have of, do we ever call the police? And the answer is often yes, if there is no other way of dealing with the threat, your job or your insurance demands it, and it isn't going to bring greater problems in its immediate wake. On an international scale that is a trickier proposition, but still, the debate is framed in such a way that seems to encourage some of the best outcomes if the hurdle of helping the rebels at all is overcome.
You do get idiots in the pro-Assad camp saying that this is Iraq all over again. But they aren't the only ones who've noticed that Iraq was a blow to the case for foreign occupations. So those from the military, like Mike Jackson on Newsnight the other night are talking about making Western involvement as much about giving weapons to the FSA as possible, and not putting Western troops in. There isn't noticeably any slippery slope, the West has done well enough not bothering to intervene so far, weapons that help turn the tide of battle are not then going to have anyone saying that the West is not doing enough.
Will America be more popular in Syria if they help the FSA? I think so, even if the help comes very late, because desperate people are grateful for help. Do I think this will give American corporations a head start in exploiting Syrian workers in the future? Yes (despite the Syrian people's antagonistic relationship with America's ally Israel), but that's inevitable when their state does good things.
The left would be advised to be practical over Syria, because if it cannot answer what can be done to improve their lot, the suspicion will be that it has nothing to say to anyone living in a non-Western backed state, and may well prefer totalitarian dungeons to any sort of democracy. And that would be a small, sad, cranky left for the foreseeable future.