Over the years, many people have critiqued the fact that the Avatar always leans towards bringing peace then bringing chaos. They believe that this is unbalanced, and that maybe the Avatar doesn't bring balance like they claim. But, this critique is something that really doesn't make sense (until post Light in the Dark). The Avatar was never going to lean towards chaos, because that's not how the Avatar keeps balance.
Contrary to what people think, the Avatarverse is naturally leaning towards chaos. This is because at the end of the Era of Raava, Vaatu was made giant, allowing for his influence to spread across the world. Because the world is always in threat of falling into chaos, the Avatar is supposed to act as a counterweight to this chaos, set on the side of peace. Wan says this himself in Beginnings Part 2:
"This is my mission: to use Raava's light spirit to guide the world toward peace."
If the Avatar is not there to be this counterweight, chaos takes over the world. This is especially seen in the early era of Aang. With his disappearance, the fire nation caused chaos to spread across the world. The Avatar (pre-Korra) brought balance by being a counterweight, not the scale itself.
This system of balance does change after season 2 of LOK. After putting Vaatu into gestation within Raava, and then re-bonding with Raava, Korra has stopped the Avatar from being a counterbalance to chaos, and now they are the scale of balance itself. With Vaatu inside them, it is now possible for Avatars to lean towards the more chaotic side to keep balance. And according to Bryke, this will probably be happening in the future.
Anyway, people need to stop misunderstanding how the Avatar keeps balance and stop saying that they do not keep balance. They do. Or at least they try to.