Perhaps a Spirit did have that kind of possibility within it, but there did exist many causes within the possibilities of such a Spirit's future that could cause it to become corrupted just like the rest.
Balancers could just as easily become the cause of that corruption taking place, as they would not discriminate too much between a Spirit and an Evil Spirit during such a chaotic era.
It would be considered a time of war or something similar, so fewer would be willing to spare a potential threat.
There were other sources of suffering that a Spirit could endure as they tried to survive, which could result in them turning into an Evil Spirit.
If there was that low of a possibility for it to have a good influence on the world in the future chaotic era, then it was better to remove it before it did become a threat or before others got to it.
If she gave it up, then the Life Energy would go to waste the moment that someone took its life.
