Sure they are! Cold and darkness make up 99.999999999999999% of the universe.
Wrong. You can never negate the extant. It was cold infinitely long before heat was ever seen, felt or even thought of, yet there could not be heat without cold. And it was dark infinitely long before light was ever seen, felt or thought of, yet, without darkness, there could be no light.
BINGO. How would you define, describe or know light if everything was light? You can only know or define light through its opposite. Thus, with goodness comes evil. The two walk hand in hand.