Let's think hypothetically about what might happen if strikes go ahead. U.S. onland intervention will surely anger al Shabaab, the Islamist militant wing that controls an alarming percentage of Somali territory and is the biggest single threat to Somali stability. Already, the Somali government is struggling to convince the country that its relatively pro-Western stance is for the greater good. That argument will lose all weight if and when the U.S. starts airstrikes. Forget about the government's effectiveness, and forget about any hopes that al Shabaab will disarm. This would fuel the fire. No, we shouldn't kneel to the demands of al Shabaab, but nor should we ignore that their ire will be taken out on the already dilapidated Somali population.
Military convoys for shipping vessels? Good idea. Invading Somalia? Bad idea. The place may have no government, but it's one of the most xenophobic countries on earth. Even a stateless country has nationalism, and even a lawless country has sovereignty. We violate Somalia's at our peril.
Update: Over at the Daily Beast, Matt Yglesias also chimes in.