You will find that people who grew up on farms or just in the country have a very different definition of "cruelty to animals". Shooting a pest animal is just a Tuesday. Not worth mentioning or remembering. Doing it with the pellet gun instead of the .22 or shotgun is because you were feeling magnanimous that day,
or you sold out and moved to the 'burbs but still don't want pests wrecking your stuff, and don't want to risk discharging a real firearm. A cat that you don't have around on purpose very well may qualify as a pest animal. Know how people complain about outdoor cats killing enormous numbers of birds? You got a bird feeder or birdhouse, and a cat is hanging around it, that's a pest animal. Got chickens, or other fowl, same ("how will a cat kill a chicken?" Well, 1. you'd be surprised, and 2. most people keep chicks inside but juvenile chickens exist and tend to live outdoors). Just prefer not to have wild predators spreading disease to your own pets or livestock, same. That it only got a pellet means this is its lucky day. Blame the people who keep breeding more damn cats than the world needs, or assholes who abandon their pets if they decide they don't want them. Listen to Bob Barker, folks.
... that out of the way, there are way too many people who do shoot stuff, and even animals, that they have no reason to and probably shouldn't, for fun. Some may be psychopaths, but I'd bet most are just actual card-carrying morons with poor impulse control. All are best avoided.