agreed, but there are rules that normal ships have to follow...some do have security forces, and tactical repulsion weapons.... but both are very expensive...
well the law of the sea is kinda tricky once you enter some ones national waters.... would you want foreign ships with armament docking in US ports? Is kind of a sticky situation... you want ships to be able to protect themselves but not be considered "war ready" vessels... I think the (I can't believe I'm gonna say this) UN needs to have a coalition of nations warships to combat the pirates... including russia and china... because everyone has a stake in free shipping lanes... it ain't gonna happen... but it's a nice pipe dream.....