First, if you knew the lore of diablo just a little bit you'd know why humans can kill demons.
Second, a werewolf/bear might just be a little more dangerous then some dude who knows karate, unless you're Chuck Norris. And i never said anything about "realistic" so i don't know where you're going with that, hell i don't even think that you do yourself.
Third, we post here because that's what forums are for either it's complain or acclaim something. Why i will buy the game ? Because I liked Diablo 1 and 2, it's not because somone doesn't like 1 or 2 class that he can't get the game.
Now you you failled on pretty much every level that there was to fail here, so maybe it's you who should go away, get some rest before you come here post some stupid crap like that.
...and you fail at not recognizing that this isn't even anything close to normal martial arts, theres pretty obviously some incredibly supernatural and magic stuff going on along with it.