There are some animals that HAVE to eat meat because they cannot be tamed to know or understand otherwise. There are also some animals whose stomach can only tolerate the meat of other animals and therefore they would be physically unable to digest a herbivorus diet. Animals eating other animals is also essential for maintaining a healthy ecosystem and for the maintaining of other habitats.
I am a vegetarian by the way.
What makes us different is the fact that we do not need meat and we can know better if we really want to. There are far greater protein sources out there than meat, all of which are better for you as well. (Tofu, myco protein products, meat free products that are made from protein, etc)
Some animals, such as dogs and cats, do not need meat and can therefore become vegetarian if their owners feel strongly enough to allow them to, and also if the animal is willing to make that change and adapt to it. Domesticated animals can do this quite easily.
It is the human factor that destroys the animal kindgom. We mass-breed cattle which is polluting the atmosphere all for the sake of meat that we don't really need.
The same applies to introducing foreign species of animals into another country. This lays waste to their ecosystem and habitats because this is not meant to happen.
I have no problem with animals eating the meat of other animals. They are not smart enough, or are not programmed with the power or the physical capabilities to, make that change like we are.
For the record, i'm not against other people eating meat either. It's their body, not mine. My concience is blood-free and that matters most to me, I would never try to force someone else to be vegetarian.