But the whole point of light & darkness is Good vs Evil. The reason is that Light, in relation to the daytime, which is life, is associated to good feelings (happiness, love, kindness, courage, determination, etc), while darkness, aka night when everyone is asleep, therefore absence of life, is associated to bad feelings (fear, anger, hate, sadness, corruption, rage, etc).
If light could be evil and darkness could be good, this division would have no meaning to whatever the conflict were, because you could have good light warriors teaming up with good dark warriors, and figthing against evil light warriors teamed with evil dark warriors.
So, to me Dark = Evil and Light = Good
That is what Mickey thought at first, but he realized that you need to except both light and darkness in the end. It makes us who we are. Even MX said as much, even though he could have been more biased towards darkness because of his speech after he took over Terra. In the end, it all comes down to your morality and what makes you as person.