1. Justification (legal and moral).
-a. Is there a conclusive proof that the Syrian government has used these weapons?
-b. Are the US officials words that 'there is a proof, but it's secret' to be taken at face value?
-c. Can the USA claim the moral high ground to be the World's policeman instead of UN?
2. Consequences (to the Syrian people and the Middle East at large).
-a. Is it possible that the Syrian people will suffer more as the result of the bombardments?
-b. Is it possible that the bombardment of Syria would trigger the wider regional war, with far more countries and casualties?
1. Justification
1.a. There is conclusive proof (at least, public). UN has not completed the investigation. And there is a number of facts that support the the theory that these were the rebels to use chemical weapons. The latter facts are completely ignored by US and european officials. They are not officially disproved.
1.b. USA has already invaded Iraq on a false pretext (of securing the WMD stockpiles), just ten years ago. This is official, there were no WMD stockpiles in Iraq whatsoever. Also, the CIA has a history of false flag operations. For example, the somewhat recently declassified CIA documents prove that the CIA has planned to commit a number of terrorist acts (including shooting down planes and sinking US ships) on US territory and blame them on Cuba, to start the invasion of Cuba. [1]
1.c. As declassified CIA documents show us, the USA has knowingly supported Saddam Hussein with military intelligence in one of the most brutal chemical attacks in the world's history (20,000 Iranian soldiers dead, many thousands permanently injured). It has supported Saddam Hussein when it was gassing Kurdish civilians in Halabja (3,200-5,000 dead; 7,000-10,000 permanently injured). [2] During the twentieth century US has supported the most brutal dictatorships in the world, including, but not limited to Augusto Pinochet (came to power with the help of USA), Mohammad Rezā Shāh Pahlavī (came to power with the help of Britain and USA), Somozas. The USA has supported Suharto's occupation of East Timor, which led to at least 100,000 deaths, according to the UN.
Now USA is supporting the dictatorships of Saudi Arabia, Bahrain, Kuwait (Man, each and every one of them has already done some brutal stuff to their people, and continues to do this).
If the US is really serious about fighting the war crimes and use of chemical weapons(which would be great!), why doesn't it prosecute it's former senior US officials that are implicated? Why doesn't it appy the same rules to it's allied dictatorships? Without answering these questions, the statements by foobarqux that the US agenda in the region has nothing to do with protecting innocent Syrian civilians seems perfectly plausible. [3]
As to legality, according to international law, US cannot bomb Syria without UN resolution.
2. Consequences
2.a. As I have written in a number of previous posts, there is a great chance that the bombings will result in many more deaths than we can possibly attribute to actions of Assad regime. This issue is the biggest and it is not addressed, which is a great red flag.
Gen. Martin Dempsey, chairman of the Joint Chiefs of Staff said that military strikes could help the opposition and put pressure on Assad, but — pointing to the last decade of war in Iraq and Afghanistan — he added, "it is not enough to simply alter the balance of military power without careful consideration of what is necessary in order to preserve a functioning state."
And he warned that if the government collapses without a viable opposition to take its place, "we could inadvertently empower extremists or unleash the very chemical weapons we seek to control." [4]
2.b. Israel is currently preparing to defend itself from a possible strike from Syria or Iran as a consequence of US bombardment of Syria. Israel, Saudi Arabia and Lebanon are all preparing their armed forces for a possible conflict. What is this if not a sign that the US and French bombardment of Syria could potentially escalate to a more atrocious conflict?
[1] https://en.wikipedia.org/wiki/Operation_Northwoods
[2] https://en.wikipedia.org/wiki/Iran%E2%80%93Iraq_War#Use_of_c...
[3] https://news.ycombinator.com/item?id=6321933
[4] http://www.foxnews.com/us/2013/08/27/us-plans-for-missile-st...
P.S.
There are not only bad answers, but bad questions, as Žižek put it in a lecture that I recently linked to. Most of the questions that you've raised in [5] are precisely the bad ones. In this post I have attempted to raise the questions that let us better understand the situation.