If you think about it, with the modern weapons that Hezbollah/Lebanon has used, we probably dont have the assets to get the people out safely. You dont want to see a US ship on fire with all those evacuees on board.
US forces can take care of themselves in the water.
I would think that the biggest concern is the people on the ground. Once the Hezzies start figuring out that things aren't going their way, they are llable to start taking hostages or worse.
There's a lot to consider right now...all I want to know is that the BEST American minds are working on it..:)