Even the first season had Amon, the guy that wanted equality between benders and non-benders. At one point we’re even shown that power was cut to a predominantly non-bender neighborhood, and when people went outside to protest to get their power turned back on, they were all rounded up and arrested. Afterwards, when Korra goes and tries to get the people that were arrested set free, she’s told
All equalist suspects are being detained indefinitely. They’ll be freed if and when the task force deems them no longer a threat.
Just in case it wasn’t clear enough by that point that non-benders were treated as second class citizens.