Darkness and Light are always balanced within. When one upsets the balance, Chaos is born, the Chaos; which is what does not belong, corrupts the force that upset the balance, and thus Corruption is born.
So as a warning to you all; tread carefully when wielding the powers of Light or Darkness, for if you are not careful, Corruption will surface within. The Corruption will then grow and as it continues to grow it will contaminate your very soul until you are turned into a beast of Chaos that will obliterate all of those you know and love.
And with their blood on your hands...well... you will never return to being Pure again.
You have been warned.