Who cares? You seem to be assuming that security force does nothing else but sit around in case of piracy. In reality, we call these people "mariners", they are trained specialists at maintaining the hardware with which they ply their trade, they know the customs and rules to follow in diverse ports of call, and they are there to provide boots on the ground and hands on tools if something goes sideways.

There is a huge difference between bodies on the boat, and no body on the boat. You cross that line, and leave no bodies on the boat to look after things, and you now have a floating puzzle full of other people's stuff, owner's of which are not necessarily going to be happy that you decided to drop their load to the bottom of the ocean to "prove a point" where you can't even guarantee that the entire point wasn't the pirates making sure some shipment didn't show up in the first place.

Hell, if it wasn't you, the shipper, making the scuttle decision, and was actually the local Navy on justification of "no negotiation", fine. Though that really just punts the issue to international waters.

No one will blame you or foster ill-will for doing everything you could and failing anyway. People will have hard feelings if you come up and say, we blew up all your stuff because those damn dirty pirates. They paid you to get their stuff from A to B, you decided C was better.

All of this "let's go unmanned" just really seems to me to be a solution looking for a problem, and not being shy about creating a few more while we're at it.