Animal Cruelty is Just Wrong

When it comes to for a probably of having a psychopath in the making, animals are often among the first targets. However, that’s not the case in this trope, where even the Big Bad guy would be upset if an animal got hurt by another person that didn't deserve it. While allowing nature to take its course on harming animals is one thing, for many who fall under this trope… as far as they’re aware of, nature is the only allowed to hurt animals since they understand about survival. Many characters would often restrict their killings of animals to either put the creature out of its misery, for food only, and/or defense… some would refuse to hurt animals -- period.

Compare to Zombie Advocate, where someone fights for the rights of non-humans. This trope is about characters who despise those who would willfully hurt an animal. It can also be part of Even Evil Has Standards since for some, if the creature doesn’t have a say, they’re could be viewed as defenseless and would leave the animal alone. This is similar to Wouldn't Hurt a Child because of the same belief on never going after the weak.

There are some Truth in Television as some criminal organization does have rules regarding animals and won't tolerate those who are cruel to them. Animal Rights groups like PETA often advocates the end to the cruelty of animals.

Compare with Pet the Dog, where an anti-hero or villain does something good for society, perhaps making sure an innocent animal is out of harm's way.

Contrast with Kick the Dog...

Shoot the Dog, where someone is forced to a questionable act because it had to be done.

Anime/Manga
""It's one thing to take people prisoner and threaten them, but when you hurt somebody, that's going too far.""
 * Elfen Lied: Lucy attacks a group of bullies for killing a puppy. The bullies did it out of pure amusement, only for them to learn it was Lucy's Berserk Button... the hard way.
 * While Team Rocket would find ways to kidnaps Pokemon creatures from others, they were shocked to see how Chimchar was treated during his time with Paul for his training regime.
 * Sonic X, Considering the fact he kidnaps animals, Dr. Eggman does have some respect for them.

Literature

 * The Berenstain Bears and the Bully: Sister Bear gets into a fight with Tuffy when she catches her attacking a baby bird.

Live-Action TV

 * The Blacklist: Raymond "Red" Reddington may still have villainous traits despite his willingness to reform, but even he has a soft-side for animals.
 * The Sopranos: Animal cruelty just so happened to be the Berserk Button of Tony Soprano. learns this one the hard way . For Tony,  Screw the money, He Has Rules.
 * In the Law & Order: Special Victims Unit episode, Born Psychopath, badass of a cop that Fin Tutuola happens to be makes a grim discovery when Toby asks for the fate of his dog, Snowball. After seeing that, Tutuola was livid and knows he couldn’t spare Toby the heartbreaking news, but serenely inform both him and his father to exit the apartment, knowing if Henry was , chances are high they could be next.
 * For Myth Busters, while insects that are destined for death by science is allowed, following the microwave poodle myth, the crew decided that it was ones of those myth best to remain an urban legend. Since then, they are a strict policy on using dummies in place of actual animals if harm is likely to be the end result. Only in myths where animals are mostly likely to be unharmed where an actual animal can be used.
 * It was doubled subverted in the Elephants Scared of Mice myth, where actual mice were place in with elephants at a Wildlife Preserve for research purpose. When a mouse was present after the elephant dung used to hide was removed, the elephants just simply moved to the other way from where they were going. Thinking it was just the movement of the dung, it was repeated without the mouse but the elephants just went on their merry way, much to the surprise of Adam and Jamie.

Western Animation

 * The Simpsons: Lisa is a strict vegetarian, though in the video game version she does allow Bart to attack an army of Mutant Dolphin since it was on the grounds of defense. In the series, Lisa's a devoted environmentalist and very strict on animal rights, including being a member of PETA.
 * Bart is the same way, but downplayed because he’s only cruel to insects. However, his Berserk Button includes anyone who dares harm any animals in his present that are above insects, especially his dog, Santa's Little Helper. Had he not been armed, Mr. Burns would’ve learned the hard way.
 * Doubled Subverted on Maggie in the film, where Krusty orders Mr. Teeny to go after her once they entered in the Simpsons’ house, only for Maggie to break a bottle in order to use as a weapon. She only backs off from any attack when Teeny runs back to Krusty after seeing that Maggie isn't as defenseless as both he and Krusty thought.