Let's make some points very clear.
Syria's government is reprehensible. It is a softer version of the north Korean crime family one-party state, but only in scale and depth of totalitarianism. Bashar Assad inherited the supreme leader role from his murderous tyrant of a father. That family, from the Alawite minority sect has run the place for my entire lifetime.
Bashar Assad loosened the screws somewhat, but has demonstrated the typical attitude of any dictator when challenged by his subjects. He wont step down, wont disband the secret police, wont abolish the state monopoly on media, wont legalise free speech, wont legalise competing political parties, wont hold elections.
He has spread nationalist-sectarian fear amongst Alawites, fearful that anything other than the dictatorship of his family will mean their slaughter. He has encouraged the view that anyone who opposes his "secular" rule, is an Islamist.
Assad's regime torture and executes political opponents, and it is clear that it has used its own military to attack civilian populations to repress political dissent. By no measure can it possibly be said to claim any moral authority, unless one adapts Mao's statement to claim morality comes from the barrel of a gun. Human Rights Watch estimated 17,000 people 'disappeared' in Syria in the first decade of his father's rule. In 1982 he bombed the city of Hama, slaughtering between 10,000 and 40,000 people as he suppressed an uprising by the Muslim Brotherhood. Yes, one can't argue that the Islamists would be better, but the indiscriminate oppression was brutal on a scale that Western "peace" advocates would usually decry.
Bear in mind Syria has previously invaded and occupied Lebanon, and assassinated Lebanese politicians. It is far from being a non-aggressive actor in the region, a point thrown by its supporters against Israel, but ignored in Syria.
Assad's regime has long been supported by the USSR and more recently Russia, and has always been anti-Western.
It is perfectly moral for Syrians to fight to overthrow this regime. It kills, torture and imprisons those who challenge it. Its apparent use of chemical weapons does cross a threshold, one of degree. As chemical weapons kill and harm over a wide area indiscriminately in a way that is almost impossible to defend against. It is a tool of mass slaughter, beyond that of conventional bombs and firearms which have very localised effects.
Providing arms or other support for the Syrian regime is being a party to this. Russia already does this, it maintains a military base there and openly supports the regime. Hardly surprising, since Russia is an authoritarian faux-democracy that arrests and imprisons its opponents, and has little compunction about using force against those challenging its corrupt corporatist crony-capitalist state.
So let's not pretend that Syria should not be subject to international intervention in its civil war, it already has it.
Similarly, Qatari, Saudi and other Arab states have been arming and funding different rebel groups. The very same states which would cite "state sovereignty" as a reason to oppose anyone interfering in their politics.
So the genie of intervention is already out of the proverbial bottle.
Should something be done?