First of all, when you get the time I would suggest you watch this documentary.
With that out of the way, I have one simple thing to way in on. So they want unmanned aircraft that can be told to attack somthing, then do so without any human control. They say that they want to make it impossible to hack these things. If thats what you want then fine, but what happens if it make a mestake? You have to be able to tell it to abort right? Any communication with the ground in regards to control means that it can be compromised. So, for it to be impossible to compromise, you have to design it in a way that once in the air, nobody gets a say in what it does. Kill switch, or uncrackable. Pick one people.
I will go kill switch any day. Rather lose a plane than have one make a mestake that costs innocent lives.