The alternative is to stay on the sidelines, leaving the opposition to the tender mercies of Assad and his patrons in Tehran who are supplying weapons, advisers, and more. They grasp that the Battle of Syria is hugely consequential. They know that the fall of Assad would be a major blow to them. By the same token, it will be a major blow to the West if, despite Washington’s pronouncements and posturing, Khamenei, with assistance from the Kremlin, rescues and restores his most valued Arab bridgehead.
Many Iran hawks insist on viewing the Syrian civil war almost entirely in terms of their hostility towards Iran. In this case, May is arguing with Andy McCarthy, who is equally convinced of the (absurdly exaggerated) Iranian threat, but even McCarthy isn’t willing to have the U.S. throw its support behind the Syrian opposition. Many Iran hawks want to make support for Syrian intervention a litmus test to prove one’s hawkishness against Iran, but even some Republicans with the most exaggerated views of the Iranian threat aren’t buying it. That is an additional indication of how unpersuasive the case for intervention in Syria is.
The West is very unlikely to suffer a “major blow” from the outcome if Western governments do not become more involved in Syria’s conflict. On the contrary, one way to make it more likely that U.S. and allied interests are harmed is to involve the U.S. and some of its allies in a Syrian proxy war that “our” side probably won’t win. The West cannot really suffer a “major blow” if Iran manages to help keep a very weakened Assad-led regime propped up. If the U.S. stays “on the sidelines” (i.e., doesn’t go out of its way to interfere in another country’s internal conflict), our government will be limiting the potential damage to the United States. After all, what American interest is served by fueling a sectarian war in Syria? Doing this serves no discernible American interest.