Light vs. Dark

The Light is more powerful than the darkness because the Light (intentionally, consciously, purposefully) serves all, it offers its gifts to all equally, unconditionally and freely whereas the Darkness only serves (intentionally) the few, the ones that serve it in return, the ones that worship it, the ones that seek to serve themselves and profit from this alliance.
This is why the Light is stronger, more powerful and it will win. 
In a world made equally of these two forces, one positive and one negative, in a perpetual dance seeking perfect balance, the totality of the forces will be slightly more positive because the Light intends to benefit all whereas the Darkness intends to benefit the few.
In the end, all truly benefit from both. The light is nurturing, life giving, expanding. The dark forces us to go within and face the fears, the unknown, learn from it and become stronger. We bring the Light into the Darkness, we turn the Dark into Light.