like, does no one ever feel this way? its weird we can kill a bunch of dwarves but it feels just wrong to kill a cat in a game
You see, the one thing everyone is united on hating is FPS death. Some players can cope with diabolically slow FPS, most just quit and start afresh. Exactly how slow is "too slow" is different from people to people but most people have a threshold below which they will not tolerate unless their fort has something really awesome going for it.
Cats accelerate the FPS death of a fort. Furthermore, they hypnotise dwarves into becoming their owners and become a fuse for tantrums when lots of cats attach to one dwarf and they all die in some horrible accident or attack. Therefore, measures are taken to limit them. Killing is the most convenient way of doing this, but locking them up in cages are another option. Tell you what though, the best option is to go to the raws and disable the infamous "cat adopts dwarf" behaviour. Then you can let the cats do whatever and see whether you can tolerate the FPS death without having to worry about the tantrum risk of having so many cats.
If this was Elona instead of DF, you would instead be heavily penalised in-game for killing cats. Different games, different attitudes.