In Washington, D.C., most politicians have a terrible track record anticipating how wars will unfold. Iraq, Afghanistan, the Persian Gulf War, Vietnam: As often as not, America's wars of choice proceed in ways that no one in charge imagined, and the best intentions of hawks do nothing to make up for the lives and treasure squandered on missions that were never likely to succeed. But no hawk ever says at the time that he or she has no idea what will happen if they get their way.
President Obama has no clue how an American act of war against Syria would unfold, because it is unknowable. Intervention poses tremendous risks, as Chairman of the Joint Chiefs of Staff General Martin Dempsey explained. "We must anticipate and be prepared for the unintended consequences of our action," he told Congress. "Should the regime's institutions collapse in the absence of a viable opposition, we could inadvertently empower extremists or unleash the very chemical weapons we seek to control." In other words, we don't know what will happen. But it could be awful. U.S. efforts to stop atrocities could even make the situation worse.
"Once we take action, we should be prepared for what comes next," he added. "Deeper involvement is hard to avoid." What would the U.S. do if the regime collapses and Islamist extremists take its place? Is it fair to ask American soldiers to risk their lives for that possible outcome?
The U.S. government could spend millions helping Syrian refugees. It could help pay for tsunami-warning systems across the Indian Ocean, or spend more funding the development of a malaria vaccine, or stop dumping agricultural commodities on poor countries in a way that stunts their economic development. There is no shortage of humanitarian suffering for us to address, if that's how we want to spend our money, and I am fine with spending more of it helping people.
But injecting bombs and cruise missiles into a civil war probably isn't the most cost effective way to help people. It is certainly the sort of humanitarian assistance most likely to make us bitter enemies, which inevitably happens when you pick a side and start killing some of the people on it.
Intervening in Syria could have catastrophic consequences for America and for the region. Non-intervention would pose no threat to us, and wouldn't preclude us from alleviating suffering elsewhere on a huge scale (and with no risk of accidentally killing innocent civilians in the process).
Hawks are most interested in humanitarian causes that can be carried out by force. There is no reason the rest of us should share their world view, given how many times it has resulted in needless slaughter on a massive scale. It's impossible to know for certain what war would bring. That is the strongest case against going to war.