cats are super adaptable, you can amputate on leg without any problem for recovery. i had to make a choice a couple of years ago between cutting my kitties front leg or letting her die of cancer, and now she is super lively and jumpy. i had to give up my pocket money for the year before to convince my parents to let her live (the ghouls) but that was possibly the best use i made of my money in my life yet.
Life's bad enough with all limbs, imagine how bad it would be with minus limbs. I shudder to think about it, just like the felines shudder when I put them down.
not everyone is chronically depressed
it's a fucking cat, man. as long as it get to have food, care, and a hot place to sleep in they are happy. they dont get existential ennui