I think the problem here is the idea of allowing those that execute pirates on the spot to also be the group that identifies the pirates. Just because someone has the P brand on the back of their hand doesn't mean they started out as a pirate.
Besides, one country's buccaneer is another country's privateer. I don't think those lines were as clear as you seem to think.
So to argue that "it's all the same" really does a disservice to the analysis here. It's not. In the past, we had clear lines of civilization: pirates and others who operated without being part of a nation-state were executed on the spot. Now, however, we want to treat anybody we meet as being all the same. That's a nice sentiment, but it ends up classifying ISIL as some weird kind of criminal organization, and it is most certainly not that kind of thing at all.