I have watched with some interest how the present White House administration is handling the whole Syria civil war thing. I will be frank: I do not envy them. That is one of those situations in foreign policy where you have several options and all of the bad. You can choose the pit of lions, tigers, or cobras.
In Syria, the US and the World basically has three options. One, we can intervene on the side of President Assad or we can intervene on the side of the rebels or we can intervene under the guise of UN neutrality, we can indirectly be involved by arming one side or the other, or we can choose to do absolutely nothing and let it all play out.
The Western world so far as chosen to largely sit it out. Russia, Iran, and the Palestinian Hezb'allah (Army of God) seem to be arming or actively helping Assad. Many of the Arab states like Saudi Arabia seem to be arming the rebels. The US and probably others have likely been sending aid and even weapons to the rebels, though very secretly and tacitly through 3rd Parties for "plausible deniability." Certainly American made weapons have turned up, generally in rebel hands.
In the West, there has been a lot of finger wagging at al-Assad for various atrocities, which is legitimate criticism. The other side has pointed out atrocities by various rebel groups as well, which is likely also legitimate criticism. The problem is that like most civil wars, no one comes out smelling like a rose. In protracted wars, often the victor ends up with a Pyhrric victory, which is a term that comes from the Greek King Pyrrhus of old, who, as legend has it, ultimately defeated the Romans in 280 BC, but he lost so many men and resources, that it might just as well have been a defeat.
In terms of modern day Syria, whoever ends up winning will at this point be a modern day King Pyrrhus because Syria has basically civil warred itself back into the Iron Age. Just take a look at the major cities the next time they have footage on the news. The cities are bombed out waste lands with buildings that are largely big piles of rubble that would otherwise be condemned in peace time and torn down. It is really anyone's guess how many people have already been killed in this madness, but its well into the 100,000+ range. 400,000 or more refugees have been created and are overrunning the camps in Jordan and other places.
I think there are at least two major reasons why the West is hesitant of getting involved. One is simply that there are several various rebel groups and armies, and none of them particularly trustworthy. Many are openly taking about creating a militant Islamic state if they come to power, many of the various groups come from various religious factions that do not like each other historically. Assad is himself from a religious group tends to be a very low social class usually. At least one major army is more secular, but they are basically promising to create a Mubarak-style Egyptian police state after the war. Right now, they all have a common enemy under the doctrine of "the enemy of my enemy is my friend" school of thought. There is really no guarantee that if Assad and his forces literally evaporated tomorrow, the civil war would continue as the various rebel groups turn on each other in a blood thirsty "last man standing" reaction unto itself. None of those end results are all that pleasant.
The other major issue that really has little to do with Syria itself is larger forces coming into conflict with each other. If Russia and Iran are arming one side (and even become actively involved), and American and the West start arming the other (and become actively involved), does this escalate into a much larger geopolitical war, writ small? I think Russia could be persuaded to be reasonable in that event, but with Iran, one never knows.
So, with all that analysis, I remain curious as to why the use of chemical weapons seems to be everyone's definition of "crossing the red line?" Assad (and probably some of the rebels that used to be in the Syrian army) have access to chemical weapons. Some have been used, though whom exactly is responsible we may never know. It is more likely that it is Assad, but who ever really knows in the fog of war?
But my question is, why is this the trigger that would otherwise get the West to become actively involved? Killing with conventional weapons is not enough? One runs into this debate in history circles with some of the tactics used in World War II. People like to bemoan the use of the nuclear bomb, but the notorious firebombing of places like Dresden actually did as much, if not more, damage, and actually ended up killing more people. Though, with firebombing, there is not the radiation fallout.
My point is that I think we need to be careful before jumping into a mess just because one weapon seems somehow more horrendous than another. I do not now what the answer is, but I do know reactionary hysterics is not.