everything works towards balance

That's about the only thing I remember from any of my middle school science classes, but it has stuck with me. Everything in nature and science works towards balance. Most often I think of the weather in terms of this. If one part of the world is flooding, it must needs be that drought occurs elsewhere.

Today, however, I got to thinking about creatures and this methodology. I heard a report that the Large Blue Butterfly, once extinct in the UK, has been reintroduced via a strand still thriving in Scandinavia to the island kingdom. Now, please don't take me to be a hater of animals, but, if everything works towards balance, is there really a need to reintroduce a species?

Apparently the LBB was dependent upon a certain variety of ant that was no longer available in the UK, and thus the LBB also died out there. Things change. Ecosystems are constantly in flux. Creatures learn to adapt to their environment, and those who don't, move on or die out. It sounds harsh, but it is a reality. The LBB died out in the UK. It couldn't make it. The species still lived in the north, so was not in danger of wholly disappearing off the face of the planet.

But so what if it were? All things come to an end at one point or another. If everything works towards balance, why single out certain species for preservation? Such notions confuse me...