The claims are:
Here the argument is simply that "might makes right", i.e. that if you're capable of something then you're justified in doing so, but with the additional caveat that one is also very self-interested. So, one is then morally justified in doing what they what to whomever they want, but - and here's the catch - only if they want to and if it suits them.
Want to make a horse carry a load until its hooves bleed? That's what it's useful for. She can't walk any more? Bullet to the head. Dog is useful? Keep it. Cat is not useful? Enjoy throwing it off a cliff and smack the ground below.
This is not a consistent moral framework.
You might be overestimating a 35 lb. beagle's protection against a 200 lb. cougar. The usefulness in this scenario is typically overestimated. A bull certainly would be more protection if one trained it, since animals like cougars are intimidated by large-size beasts. And yet we slaughter cows. Also, if a baby is less useful for defense than a dog, can I now slaughter them? Or if there's a dog and a infant in a burning building - I'm supposed to save the dog because it's more useful at that moment. Unless... you know... I need something that only a infant can deliver for some reason.
How many mountain lions have you encountered in your life? Why do you need protection from mountain lions, why not sharks?
Also, not that this should even matter, but on the basis of this absurd scenario, wouldn't actually it make more sense to have an animal that runs slow that you can outrun that can essentially sacrifice itself to the cougar? Most dogs will probably run from the mountain lion that's literally seven times its size, and a race between you and a beagle is not even going to be close; you're lunch.
Even if we assume a dog protects humans from mountain lions and if this is a coherent metric, consider that a basic firearm offers significantly more protection than a dog. So then would it be morally permissible to eat a dog as long as you own a gun? And if you had to, say, pawn the gun for a vet bill towards saving your dog's life, would you say that it's morally reprehensible to give up the gun, your protection against mountain lions, to save the dog? This just isn't a coherent position. The mere ownership of a gun shouldn't morally impact whether or not one can eat a dog.
So if morality is based solely on usefulness - how do you think you would do if someone you didn't like were allowed to design the test? Specifically, a list of characteristics, and if you lack those characteristics, you have no moral worth in the books - they're allowed to murder you and won't feel bad about it? Suddenly this seems only like a good idea when you're allowed to design the usefulness test - which is again, might makes right as well as special pleading.