Except that the Dark comes from Dark Matter and that means that means that it's ENERGY WHICH DOESN'T INTERACT WITH EM WAVES argggggggggghhh. Besides, the "darkness" of energy is a far deeper, mysterious one than Matter; there's a lot of possible candidates for Dark Matter and experiments used to test theories regarding it and far more "out there" theories involving energy. Call it VOID ENERGY if you have to appeal to your inner twelve year old but Dark Energy just feels off in all sorts of ways.
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You're messing with me! You're messing with me, aren't you!?
You're making fun of me, aren't you!? Aren't you!? You definitely are! I'll murder you!