Actually they are worse than pirates, pirates really only want your money, well and perhaps your women. These guys just want to kill us. Perhaps better than a declaration of war would be a formal declaration from Congress, and signed by the President, that they are "enemies of the United States". That would have the same effect domestically and would allow us to treat them like pirates were once treated, that is "shoot on sight".
If these scum didn't have information value to be "squeezed" out of them, I would gladly say "Shoot them on sight". Bullets are cheaper than trials and the waste of "panty" torture.