A warship coming to dock in peace is a different beast than one in a defensive posture.

Right now the pirates are bloodsucking ticks: irritating and noxious but tolerable in small numbers. It is only a matter of time before the pirates overplay their gambit and the local populace suffers the result. Fumigation will kill the ladybugs along with the ticks, to stretch the analogy.

I think they chose poorly when they took the Russian arms ship. Eventually a situation will escalate and the pirates' den will be cleared, and perhaps much of the Somalia coast with it. It will probably not be the US though -- we'd just do an escort service instead.