Though I’m not entirely sold, I found Jamie Rubin’s case for intervention in the Syrian civil war intriguing:

It is the strategic relationship between the Islamic Republic and the Assad regime that makes it possible for Iran to undermine Israel’s security. Over the three decades of hostility between Iran and Israel, a direct military confrontation has never occurred — but through Hezbollah, which is sustained and trained by Iran via Syria, the Islamic Republic has proven able to threaten Israeli security interests.
The collapse of the Assad regime would sunder this dangerous alliance. Defense Minister Ehud Barak, arguably the most important Israeli decision-maker on this question, recently told CNN’s Christiane Amanpour that the Assad regime’s fall “will be a major blow to the radical axis, major blow to Iran…. It’s the only kind of outpost of the Iranian influence in the Arab world … and it will weaken dramatically both Hezbollah in Lebanon and Hamas and Islamic Jihad in Gaza.”

This would certainly be a desirable outcome, though it is worth noting that Iraq is also subject to Iranian influence of a kind.