It’s not just the hideous atrocities of Assad, father and son. Walter Russell Mead makes the argument in a superb post on the Syrian situation on his blog:
Regime change in Syria would greatly increase the chance that Iran might come to its senses. The shock of Assad’s downfall might rekindle the enthusiasm of the democracy protesters in Tehran; alone and friendless, a rattled Iran might be more willing to compromise on the nuclear issue. Either way, there is a good chance that regime change in Syria would reduce the likelihood of a major confrontation between the US and Iran.
From a US point of view, regime change in Damascus has several possible upsides. There is not only the sobering and isolating effect on Iran. Regime change would likely strengthen the moderate camp among Palestinians (including the more realistic elements in Hamas) and could improve the chances for Israeli-Palestinian peace. It would substantially reduce the chance of new Hezbollah attacks on Israel and could open the door toward a more effective and more democratic government in Lebanon as well as Syria.
Read it all.