I hear ya. Its probably not a lot in an economic sense. And while I am all for cost benefit analysis, sometimes sending a message has a larger effect that transcends economics or ultimately helps economically in other regions. If we show we are willing to dtand up to threats, the Russians, Chinese and other enemies may think twice before trying something. When we project weakness and indecision we get attacked. Look at Pearl Harbor, 9/11 after eight years of Clinton, the hostage crises during Jimmy Carter.
Nothing wrong with sending a message - it's a limited "one-time" effort that hopefully gets the point across and serves as a deterrent.
Did that really happen here, though? If you want to send a message, you just shoot the people at the first opportunity (which, maybe this was, although I doubt it), instead of calling in the FBI (seriously?) to negotiate.
But, that's not really how it works. Think about how you do with a dog - you get mad and yell at the dog, and she goes and hangs her head...and a day later eats your sandwhich off the counter again. If I want to keep her from eating my sandwhich all the time, I can either never leave the counter alone, never have a sandwhich, or put the sandwhich elsewhere. Which one makes the most sense? People aren't too much different from that.
In other words, unless we want to keep a permanent naval presence within X hours steaming of any potential pirate activity anywhere, it ain't gonna do any good. So, let's think of some more creative solutions other than "let's blow them all up," because we just don't have the resources for it even if it were possible.
The idea off the top of my head? Mandate a basic course in ship defense, and provide an actual defensive capability, for the crews of all American-flagged ships; revise the maritime laws to allow for armed ships (at least those frequenting the sketchy parts of the world). Expensive and time consuming? Yes. But, when it's passed on to the consumers, it's pennies on the thousand-dollars. Does it solve the problem? Probably not, but it'll be more efficient and cheaper than calling up the Navy every time there's a problem.