Instead of Amon killing benders and the avatar he took away their bending he was a bad person no doubt about that but at least he did not kill. I know Amon would sometimes go as far as to kill but did not.
"Not killing" gave him justification he needed. But even if he would take everyone's bending, he would still be a bender and the world would still be unjust, his goal was unatainable from start, but admirable for sure.
