when i watched the first season i came up with a neat way that Amon could have removed people's bending.

it is mentioned in the finale of the last airbender that ancient benders used to bend the energy within people instead of the elements, and that this energy-bending is a practice lost to time. but the lion-turtle, one of the oldest living creatures inhabiting the show's universe, was present during this time and teaches it to Aang.

we also learn in the finale of the first season of the last airbender that Koh, the face-stealer, is the oldest living spirit. hence Amon, in his studies, discovers the existence of energy bending and makes a trek to the spirit world, much like Iroh once did before him, to see if Koh might know. Koh offers to teach him, but at a cost--his face. this is why Amon wears a mask, because he gave up his face to learn the ancient art of energy-bending

i like my theory better than the show's explanation tbh.