>>54676357IRL, we react appropriately to secondary signs of health/fertility. A giant forehead reminds us of balding, and feels like a lack of health (at least for women). With cartoons, we take away that reality, and so things that are physically but not conceptually appalling suddenly become OK. This is also why things like MILFs, musclegirls, or traps are WAY more popular in cartoons than IRL.
So a 5head in anime isn't activating our physical response to avoid it, and all that's left is maybe how it's funny, or cute despite it.
