[GolurkIsDaBomb]

@~Harmony

Spoiler:

I think the point they tried to make in the last episode was that it wasn't energy-bending, but bloodbending. Since Noatak (don't know if that's spelled right) thought the avatar was the most powerful, it makes sense that he'd do his best to try and "recreate" the most powerful form of bending (in his eyes). However, he must of not been able to find a teacher so he used bloodbending to do the job. I think he closed the physical, biological part of the brain that allows bending, but not the spiritual side like Aang did (which is why Korra could airbend, the most spiritually connected of the elements) This is also why I think it could be reversed unlike true energybending.