Why do you say it' s 'completely unreasonable' to deny some individuals rights? Does that include insects or even plants? If not, then how do you decide who deserves to have certain rights and who doesn't?

How about rats then, for example? Nobody bats an eye when rats get poisoned. Nevertheless, rats are incredibly intelligent animals and they care about each other/their owners. So then why is poisoning rats okay, but killing cats makes you a monster?

Clearly, as /u/hacksoncode pointed out, our morality is just something that evolved to benefit our species. Organisms are little more than extremely complicate machines that programmed themselves through evolution.

An example that came up recently was torture (waterboarding) and the U.S. using it on terrorists to extract information. Is torture really inherently wrong? If you waterboard someone, all you do is create a certain stimuli which will cause a reaction in the other person's body that will make him experience pain/fear, which is our body's way of making sure we try to escape from a certain situation and avoid that situation in the future. This is a handy little trick to make someone give you information. When it comes down to it, it's just one organism figuring out how another organism functions and using that for its own benefit. There isn't anything inherently evil about it.

Things have a certain mass and a certain size. But whether or not something is immoral/evil/wrong is just a fabrication of our minds, and the result of genetics and the environment we live in. The reason we care about cats and dogs is that we do, and the reason we don't care about cows is that we don't. All you can do is analyze our morality and try to figure out why it evolved in a certain way.