It's not an argument until you turn into a snowflake over a dissenting opinion.
Yeah, all people are animals... by definition. And no people are animals... by definition. I think it's pretty significant, but then, I actually think about things. Labels that ignore people's humanity -- animal, monster, demon, chick, Canadian -- run the risk of forgetting that connection to us and any emphasis on prevention, redemption, thoughtfulness, intelligence, humility, etc. Those labels can truncate consideration of what led to it or any effort to do anything requiring effort that might help.
And at what cost? I can hold someone accountable without having to turn them into the ugliest caricature possible, especially if that's all emotion that obscures some other lesson. I mean, in studying WW2, if we portray all Germans as evil incarnate, we might forget that the Treaty of Versailles exacerbated things, that desperation sets the stage for embracing extremism, and that indoctrination is a formidable tool. And then we might perpetrate another Treaty of Versailles, or fail to offer an alternative to extremism before people are driven there, or to ignore signs of creeping indoctrination. Meanwhile, we can still be conscious of all of those things while exacting justice just as firmly and fairly, and more productively than before.
Note I'm parsing the potential extremism in my own words: "run the risk," "can truncate," "might forget," "might perpetrate." If you want to respond like a big boy, you could just say, "Duly noted. I'll keep that in mind while continuing to call them 'monsters,' recognizing my own hyperbole for what it is, and attempting to emulate Dat's calm intellect whenever I can manage it." Or you can keep whining and calling liberals names.