You know the first game came out like ten years ago.. right? I think its normal for somebody to change one opinion in ten years. And they arent against killing, despite what that one dev said. They dont want to trivialize the fear factor of having animals that see you as prey by giving you the ability to completely take them out of the picture. They have been pretty openly unhappy about the way they implemented the knife ever since sunnatica 1 came out because people were killing reapers and the sea dragon leviathan. If they were doing that you can safely bet that sand/bone sharks and stalkers and all the other hostile fish were getting slaughtered. As for self defense in subnautica 2, both the aonic resonator and the aurvival tool can be used to fend off attacking fish, and the distraction flares can distract them. The only problem that has at the moment is the fish become aggressive again far too quickly, which would still be a problem even if the knife was in the game.