"Idiocy. They are all sentient beings to varying degrees, they're just obviously not as "smart" as you [think you are], so in your world, anything goes right?!"
They aren't human beings.
He made a great point in asking why do some people scream about human on animal cruelty when they turn a blind eye to human on human cruelty. That doesn't make him a clown, it makes him something that refuses to treated like one.
Human beings have dominion over all the animals whether you know it or not, but that doesn't mean we act in a cruel fashion or destroy them all. It just means they're ours to do with as we please. Comparing people to animals is cruel in my book, because it hints at the fact that you think have dominion over people.
Animals certainly have emotions and feel pain, but that won't stop me from eating them, and if you aren't careful, you'll convince me that you're just an animal as well, something that can be controlled through your emotions and through pain.
Maybe that's why you thought you could control him by calling him an incompassionate idiot and a clown? You thought you could win by causing him pain?