Syria is a major strategic piece in the region. toppling that regime would severely curtail Iranian operations.
I don't think that is clear for a number of reasons:
1) Who would take over a post-Assad Syria? No specific names are known.
2) Is the leader-in-waiting legitimate and could he/she exert sufficient control to maintain stability? No specific leader is known, so that question is unresolved.
3) What specific policies toward the U.S., U.S. regional interests, and U.S. regional allies would be undertaken? No government-in-waiting exists, so that's not clear either.
4) What institutional structure would assure that Syria would not disintegrate, leading to further regional destablization and developments that could lead to opportunities that could be exploited by Iran or Iran's non-state allies?
The outcomes in Egypt and Libya did not lead to liberal democracy. To date, there's no concrete evidence that the materially enhanced U.S. interests. Indeed, the early developments in Egypt have raised concerns about the Egypt-Israel peace agreement that is of major importance to U.S. regional interests. Fortunately, Egypt's military has applied the brakes to the kind of rapid transformation that could have taken Egypt down a path that would be even worse for U.S. interests. In Libya, the post-Gadhafi government has done little to bolster U.S. interests and has continued to protect the Lockerbie bomber from extradition.
IMO, the absence of clear answers to the above four questions and lack of compelling U.S. interests that would override that ambiguity suggest that the U.S. should not intervene militarily. The Assad regime's brutality is not sufficient to warrant a military response that would not lead to a marked enhancement of U.S. interests or those of its regional allies (moderate Arab states + Israel). In the end, I fully agree that Syria is a major strategic piece (relationships vis-a-vis Iran, non-state actors in the region, and Lebanon), but don't see U.S. military intervention dramatically changing Syria's strategic role in the region on account of a lack of identifiable and legitimate successor government-in-waiting. As a result, military intervention would amount to a roll of the dice, with only the hope that a successor government would be better for U.S. interests.
