I've see a lot of people ragging on snake owners the last while on this site but almost never see posts targeting more "normal" pets and their owners who are likely doing worse. Yes I believe raising animals in poor conditions and feeding them live (if its not an absolute necessity) or killing them in cruel ways is wrong, but I don't think the feeding of animals is inherently wrong. Its natural and sometimes unavoidable. I've volunteered with both domestic and wild animal shelters- in the wild shelters sometimes you have to raise "feeder" animals to rehabilitate the wild ones, birds of prey need their meat, owls need the whole mice for example. Shelters are often highly limited by their funds and buying feeders all the time can be out of the question, so you have to breed your own. Besides, there are far worse, and far more common things going on than a few assholes feeding live animals to their snakes for the fun of it.
For example, so many people think it is okay to let their pets run around loose outside (even if they're not fixed). Even worse is how little people seem to care, or that they think (especially in the case of cats) that not doing that is cruel for their animal. There was a fellow at another place I volunteer at, reminiscing about his dog, who wasn't fixed, running about impregnating the other dogs in the area, and acting PROUD of it. Like that's my boy, he was such a stud, and no one seemed to be upset about this.
With cats no matter how cute and fluffy it might be, if you let it outside there is a good chance it will kill things (at least 30% of outdoor pet cats kill, on average, 2 or more animals per week). And it likely wont even eat them, THAT is cruel in my mind. Wild animals shouldn't be having to face your pet, they've got enough to deal with already, and they're not part of its natural food-chain. Then if they don't die immediately, they're injured, suffer, and die from something else, or they're rescued and put strain on wildlife shelters. This is a completely avoidable death and they're often prolonged deaths (have you ever seen a cat play with a mouse?). The maybe a minute a snake would take to kill a live animal (which I'm still not condoning feeding) is far less cruel than what many cats put their prey through. It is estimated cats, in the US alone, kill over 4 billion animals a year. 4 BILLION, and these aren't animals raised to be food, these are wild animals and their deaths could be messing up ecosystems or endangering species.
Its also dangerous to your animal, be it dogs, coyotes, cars, even other individuals of the same species. Many people seem to forget the spread of disease. Cats get AIDs. You let your animal outside, it can easily contract feline aids. Sexually, fighting, sniffing noises, getting spit on, even stepping in infected fluids and cleaning their paw can cause them to contract FIV (feline version of HIV). Do you want to expose your animal to this? It can bring it home to other cats as well, and potentially infect later adopts after your infected pet passes. There are plenty of other potentially fatal diseases too.
Humanly raising feeder animals, killing them humanely and feeding them to a herp isn't nearly as bad in my mind. Do I dislike cats? Not at all, I think they're wonderful critters, I just don't think their place is outside, especially so when not supervised, for their safety, other pets, and that of wildlife.
I'd also like to mention that people looking for animals on craigslist to feed to their pets may still kill the animal humanely before feeding, they might just be looking for a cheaper alternative than the store. Would I want my pets fed to a snake? No, of course not, that's why if god forbid I had to rehome, I'd make sure I'd put an adopting fee and screen potential adopters to avoid people who just want them to feed to something else. But does everyone care? Likely not. Enough people let their pets go outside to speak for that.
I've read a few posts about only feeding diseased/dying animals/death row animals. Other than the last option the other two boarder between impossible and cruel. It should be noted the last option is effectively getting free pets off craigslist anyway. Most pets that aren't adopted and end up at a normal shelter, will likely be put down and then destroyed, never to be used by another animal, and just become landfill or ashes, which is a real waste (both in terms of their life, and their bodies). When it comes to diseased or dying animals (say from old age) it could be cruel to leave the animals suffering while finding someone who wants to take them, humanely kill them, and feed them to their pet. Sure you could freeze them in the mean time to put them out of their misery, but many people want or need them fresh. Also, people who've kept their pets long enough to die of old age are unlikely to give up their pet at the end to be fed to something, they'd probably prefer to be there for its last moments and bury it or get it cremated. Additionally, most of the carnivorous pet owners likely wouldn't want to feed diseased/dying pets since, well, that just isn't appealing. Maybe they would eat the inferior animals in the wild, but these aren't wild animals and the disease could be infectious. I ask cat/dog owners, if you saw a bag of food that said "Contains meat products from only diseased or dying animals" would you really want to buy that? Do you think other people would? I wouldn't personally, even if its likely processed through the roof I still don't know what they were sick/dying from and wouldn't want to risk exposing my pet to the potential rare disease that could make mine ill. Sure they're probably already in my pet's food, but its a bit different being the main component. If you don't like that idea why would you subject another pet owner (and their animal) to that?