system
A chat on subreddit /r/NoStupidQuestions
human
Really, once you get to mammals especially, it isn't really about how close they are to humans intellectually or genetically, but how close we are to them emotionally.  We have a deep personal bond of friendship with dogs, cats, and horses.  Less so with "livestock" type food animals, and even less so with wildlife and "pest" mammals.  These relationships have very little to do with the intelligence of the species but they have everything to do with how we view  hunting, killing, and eating that species.
gpt
Another important factor is aesthetic appeal/cuteness. Killing almost all bugs is normal, but deliberately squishing a butterfly or ladybug would make you look kind of insane.