I think you're exaggerating. Demons are demons, not angels or fairies. They're supposed to be scary. And since the game has a 12+ rating, it means that the ESRB (European Rating Board) has already reviewed the game and assigned it an appropriate rating. Also, the information about the Tormentors clearly states that they inflict pain on themselves to increase their hatred towards others.
Added 4 minutes later
Quantity is what matters here. And so far, I've only seen the volcanic/stone style on the upgraded Cerberus and Juggernauts. But the Tormentors and Pit Lords are made of flesh. Maybe people are specifically creating weapons for demons:D (if it kills demons, then it's even better against others).
Цикл "Закадычные враги": "Особенное гостеприимство, "Супероружие", "Меж молотом и наковальней"
"Падение Шантири"
Кампания для "Кодекса Войны"
"Выбор Сагиттеля"