This article from the Military Times shows that 75% of United States military troops, including many higher officials and commanders, oppose the air strike of Syria.
This shows that the majority of the citizens of the United States, the members of the U.S. military, and the leaders of the world all oppose a potential warfare between the U.S. and Syria.
Would Obama make the decision to strike despite so much opposition? If he does, the political message of such a decision would be that the U.S. will not listen to either its citizens, its military members, or other key country leaders. Therefore, at least from a formal political perspective, there really isn't any justification for the U.S. to strike Syria.
How about more rational reasons with regards to the decision itself, keeping in mind, of course, that in politics form matters just as much as the pure content of a decision? In this case, the Military Times article provides an interesting comparison between those reasons given for and against the airstrikes.
As for cons, military members point out the fact that the United States is economically not in a position to invest in another war that would take years. It also tries to appeal to psychological reasons, such as the fact that those who are actually fighting the war are getting weary of engaging in endless battles. Finally, troops point out the fact that to engage in another war under the present formal political conditions would worsen U.S. isolationism, which is not a very attractive course of action when there is another option, that of the U.S. letting the "rest of the world figure out what to do" and thus playing a supportive or a more dynamic role in world politics rather than always being Big Daddy. In addition, troops point out strategic problems related to supporting the Syrian rebels, which might be an irrational thing to do given how those Syrians can potentially turn into another group of insurgents.
On the pros side, the main reason is a "humanitarian" or moral one. The argument runs that to strike or not to strike will directly reflect on the United State's moral standpoint against the kind of violence that took place in Syria.
If we now weigh the two sides, it starts to seem that there cannot really be a rational justification for the strikes from a political point of view. In politics, while how a country appears to other countries and to its own citizens is an important political element, other more concrete issues such as economics and military strategy ought to be given priority. A country does not follow any pre-established moral rule, but rather is in a position to define for its citizens what counts as moral. Thus, there is no moral a priori justification that can ground a political decision, regardless of how complex the decision might be.
Incidentally, it is apparently quite rare that the United States military members oppose a war even before it is being fought. This historical novelty also ought to signal a warning for U.S. leaders.
However, despite these considerations, I do think that there is a strong chance that the U.S. leaders will decide to force through their decision to strike Syria. Why?
There is no reason that they can appeal to in this decision, but there is a cause (the distinction is crucial here.) The cause would mostly be psychological, pertaining to the frame of mind of the leaders in charge.
Naomi Klein's The Shock Doctrine shows how and why many country leaders, including U.S. presidents, lose their rational control over political situations and momentarily turn into irrational decision-makers. The sense of "urgency," coupled with a sophistical (= convincing yet baseless on a more critical analysis) rhetoric that makes them think that the war is "needed," together with high levels of stress (from which the only way to escape is to "make a decision" - as far as this is not made, they will have to withstand continual pressure; this seems to show that it really requires more strength, character, and leadership to not do something rather than to do it) equals recipe for irrationality. Moreover, the case of Syria is reminiscent of the Iraq War on several levels. The symptoms are all there, and one suspects that the particular interests of the weapons industry, as well as the need to maintain "social cohesion" in times where Occupy Wall Street and other dissension continue to express criticism against the government, are involved in these recent happenings.
Therefore, while it might be true that the Syrian government actually used chemical weapons against its citizens, this is not a good enough reason for Uncle Sam to lift his buttocks and fight. Nonetheless, he might be induced to doing just that. I wonder whether president Obama and his advisory board members are aware of Klein's work, and how past leaders have made wrong decisions in situations like this.
Postscript: After reading several more articles which provide different perspectives, I'm also convinced that another possibility exists with regards to how to interpret Obama's decisions thus far made. The antiwar.com articles such as this and this suggest that Obama's very aggressive gestures might actually have positive effects with regards to the peace politics between the United States and the Middle Eastern countries. If this really is the case, then we'll continue to see Obama walking on a thin line that divides war and peace, but never crossing it completely until the peace process comes to maturity. At least it feels good to think that the prospect of striking Syria is not merely there as a trap into which leaders may fall but also as an effective diplomacy card.