This is a very poor example as to why humanity is shit. There are many better examples, the best of which are too controversial for the internet. However, I would definitely save my pet. Whatever animal it may be, I would have responsibility to save it because if it can't swim, that isn't my pet's fault. It just didn't learn it because maybe it never experienced deep water before, or it's an animal that evolutionarily has never been able to swim (I'm humouring the idea that an animal couldn't swim, most can). Whereas, unless this human stranger was a young child who hadn't had chance to learn to swim properly yet (if so there would be a parent or carer around, surely), they should be able to swim. It is not my fault if they didn't take the time to learn as it's an important skill for survival. Plus if they can't swim, they're an idiot for getting themselves into a situation where they might end up in deep water without any safeguard. Any kind of idiot does not deserve to be saved in such a situation. To summarise: a pet is your responsibility, of course you'd save them. Idiocy is the foundation that makes humanity so shit. It is the sole reason for most of our drawbacks. It is merely compounded by various other characteristics such as greed. Logic will out.