I personally think:
- When you are in hostile/war the only KD you take gc from is your opponent since that's pure 1vs1
- When you're not in war/hostile you try to avoid stealing/hitting into someone else hostile/war as much as possible. Here you can ofc discuss what is called hostile and what isn't, but that's not the question. (Eye for an eye can be an exception here)

My rule is mainly: don't do to others what you don't want others to do to you.