Having rules for harming and killing people and destroying things seems weird, but not as weird as not having them. We do have some rules about harming and killing in the physical world, but we don't have any for the intangible digital world. We need rules for cyberwar badly.
These will require some uncomfortable acknowledgements, some unlikely agreement across cultures, and probably some disaster to happen first.
Like all things digital, it's a knotty, complex, tricky problem. Boundaries in cyberspace are inherently blurred to non-existence. Motives matter more and are harder to screen apriori. The list of difficulties goes on and on.
But I am sure of two things: having rules of cyberwar will make ordinary life online more secure, and it will also increase peace in the physical world.
The best first start I've seen in creating rules for cyberwar are outlined in this IEEE article: "It's time for Rules of Cyberwar"