Well, a fringe movement known as the Equalists that likes to blame benders for all the ills facing society stopped being fringe and started gaining far too much traction when a new leader arose who could basically remove people’s ability to bend. Now, the previous Avatar was able to do this as well, but he was effectively the only person in history who could and he only reserved it for the most dangerous possible cases, like the warmongering former ruler of the Fire Nation and a violent criminal whose unique bending ability would render him impossible to imprison otherwise.

The Equalists’ leader, Amon, basically declared war on all benders and has set out to sever everyone’s connection to the elements regardless of their moral standing or their place in society. He believes that the ability to bend in and of itself results in benders oppressing those who can’t bend, even if actually opening your eyes and looking at the state of Republic City would tell you that isn’t the case. Logic doesn’t actually have that much of a place in this kind of thing, though, especially when you’ve got some kind of charismatic cult leader heading things who can actually produce tangible results.