Also, pirates would become a problem because taking over a ship without a crew would easier and way less risk.
Consider patrol drones. They look nothing like something an individual can get into.
Besides which, an automated ship is about a trio of tugs, a computer replacement, and a buncha fuel away from anywhere.
You mean deliberately sink a $10 million ship, causing a massive environmental disaster. Not to mention being a hazard to other shipping if the water is shallow enough or the ship breaks apart.
Do you blow up a grocery store because someone attempts to steal a jar of pickles?
The question for an insurance company isn’t just about this ship, but the cost of paying out future hijackings. On top of this there is the rather more interesting option of refloating the ship.
As to DDoS, sinking isn’t any more of a risk than someone taking over control of your self driving boat and aiming it at the coastline. From a pure safety standpoint you need some method of remotely disabling the ship.
The ships can be worth quite a bit when new, but their also depreciating assets with only a few percent of that in scrap value. Only using the least valuable ships in areas that can be pirates seems like an obvious optimization.
At the same time actively preventing piracy is expensive. Having a significant armed security force on a boat is effective, but paying for them when 99.999% of the time when their not needed isn’t cost effective. Making it clear that attacking a ship is pointless on the other hand is a great way to avoid getting attacked in the first place, but you need to be willing to carry through.
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.
About pirates, no, they work will become much harder if you don't have anybody they can point a gun to and tell to stop the ship.
The city of Ghent was eyeing autonomous small crafts as "water taxis", and a big shipping provider wanted to do last-mile(s) delivery for shops, restaurants, and small parcel pickup points along a river. For the latter case, the vessel would still be manned, but instead of having to navigate, that person could sort and prepare parcels for delivery.
Also, a significant amount of money is spent providing 24 hour cover of navigation in the bridge so I guess you could save something by automating a lot of it.
You are probably right that in the extreme, it would be better to have some humans to make sure your containers make it to their destination!