This is going to sound weird, but when people say that darkness is evil, i'd rather say that in most cases it can be considered as a very "unpredictable" element when reffering to its morality.
this may be a lame example but still should be considered highly:
From DC comics, Batman is a well known hero, Yet he is a very dark hero, If you've noticed, He usually only lurks in the dark when fighting crime, perhaps marking his dominant strategy and trait, If he knows he has to actually kill someone for the sake of Justice or even his own views on it for being the best option in the given situation,
He would NEVER hesitate and just go on ahead.
(this makes Superman look like a wimp IMO, Which Is why i like batman)
However in some cases he has been shown to be more neutral, as in sometimes not wanting to help the justice league because of his different views. Morality never gets in the way of Batman's objective (again, anti-superman)
He may be very stubborn and can get quite abnoxious, but that stubborness and Abnoxiousness is also linked with his amazing genius level IQ, therefore possibly making him one of the or even THE smartest hero in DC universe.
And his nature is based on that of a Dark one, unfriendly but extremely intelligent.
Therefore, I could relate this type of persona to
And therefore use this as an example in relation to why Labeling Darkness as "Evil" is just simply an irrational way of thinking, darkness has many properties than just being a stereotypical (invalid) sense of evil. Just because Darkness has its own perspective of things Just as Batman always has his own perspective of things, doesn't make it "Evil".