[@Rabidporcupine]
Hm, that's very true.

There's a few aspects to consider. First, all the other monsters are, despite their human-level sapience, still different species. Humanity is no stranger to eating intelligent animals, of which pork is a prime example. And we're not wholly averse to using parts of our [i]own[/i] species for irreverent uses; human bones are a preferred instrument in leatherworking, for example, and some of the modern stem cell research uses aborted human embryos. And, whether the monsters have human-sapience or not, everything's fair game when they're out for your blood. You gotta defend yourself.

Now, all that said, that the monsters are "humans in different bodies" is merely headcanon. Current literary convention has the different species at different levels of sapience, which is inconsistent with broad-spectrum humanity. So at most, I could see there being an in-universe conversation about the morality of eating creatures with sapience approaching ours, but at the end of the day, they're not (considered?) human.