There's a big disclaimer in this page that warns about animal violence. Why did you play the game if you can't stand that kind of content? You're punishing the dev for something that is entirely your fault...
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I wish common sense was common enough that I didn't have to mention this - it's ok to not like certain types of content, however, it's important to note that videogames are NOT real. Those cats aren't real. Those people aren't real. You can't hurt something that doesn't exist.
Most people know that fiction is just a story medium; to experience new things, new perspectives, or merely a form of entertainment. Immoral acts are permissible in fiction because they have no bearing in reality. Similarly, the inclusion of dark topics doesn't necessarily mean either the player or the author approve of such things in the real world.