What if over time the legend have been distorted and The Others are just the children of the forest that fought against the first men/andals, and over thousands of years the legends got distorted untill we had the "benevolent" but extinct CoTF and the Others. Hasn't GRRM even said that the others aren't necessarily wholly bad? I mean, its even in the name- they're the "Other" children of the forest, the ones that are left after the invasion.

My theory: The Children of the Forest were driven North by the Andals, who were kind of ruthlessly killing them for not reason. Then the Andals rubbed salt in the wound by building a huge-ass wall and telling them to fuck off. It kind of makes sense for them to be a little pissed off at them.

They want revenge on humanity for driving them out of Westeros and industrializing everything, cutting down the trees that were their homes and such. The cold weather up north, combined with their anger, eventually lead them to transform into Wights. Using their magical power to reanimate the dead, they built up an army. I mean if you look at the backstory, the Andals were kind of giant dicks to them. Also, I marked it aSoS because thats where I'm up to so please use spoiler markers freely!

Edit 1: Credit to /u/TheCakeIsLegit for helping me with evidence, I directly quoted some of this from our chat! :)