Amon unmasked (theory)
I think Amon really is Bumi (Aang and Katara's son), as he is the only non-bender in the family (His father Aang was an airbender, mother Katara-waterbender, brother Tenzin-airbender and sister Kya-waterbender) he might have had a secret grudge against benders and gone evil. And as he is Aang's son he could have inherited Aang's ability to take away bending, as Tarrlok inherited his fathers, Yakone's ability to bloodbend without full moon.
Who Amon probably is
I think the Amon really is Bumi (Aang and Katara's son), and because he was the only non-bender in his family (His father Aang was an airbender,mother Katara-waterbender,brother Tenzin-airbender,sister Kya-waterbender) he may hold a grudge against benders. And as he is Aangs son he could have inherited his fathers ability to take bending away, like Tarrlok inherited his fathers, Yakone's power to bloodbend without full moon.