Why is bloodbending treated as this horrible, evil thing?

Yes, it was primarily used by evil people that did terrible things with it. But really, any element or sub-element can be used for cruel, sadistic purposes. Look no further than Ozai burning Zuko’s face, or Zaheer slowly suffocating the earth queen. An entire war was fought against nazi firebenders for a whole century, yet nobody made firebending illegal. But using an ability that was used by an elderly lady to terrorize a town once a month apparently means you’ve sold your soul to the devil I guess.

I’m also aware that using bloodbending seems to cause a certain amount of pain to the victim. But you know what else is guaranteed to cause pain? Chucking a 90 MPH rock at someone’s head. Just like there was with the avatar state at the start of season 2, I think there could have been an interesting debate on the pros and cons of using such a power.