Wait, did you all not kill stuff in the first game?

Seeing talk about the lack of fish-killing for Sub2 has me confused. The decision itself is not at all my cup of tea, but I am also seeing a lot of comments to the effect of "of course nobody wants to kill the Leviathans, but it would be nice to have deterrents".

*Do* none of you want to kill the leviathans? Were most of you just running away from them in Sub1, even in late game?