clap, clap, clap Bravo. Only a death so close to Harry could make Harry feel powerless. Add in anger over the wedding not even being finished, his best friend's brother's death, and an utter feeling of hopelessness to help, he turns to the Minions and actually is Dark.
I'm glad Harry tried to turn away from evil, only for him to embrace it later. It's very realistic for Harry.
Granted, I still see him as hesitant to do any of the more evil deeds the overlord position will require...at first. He needs to justify it to himself. For now he will focus on the war. And the deeper into the war effort he gets, the less "good" he will see in the so called "light" side.
Those who claim to be good rarely see how their actions affect the world around them as they see their own justified deeds. I think the Harry in the books, well by the time the seventh one came around, was completely incapable of realizing that he himself wasn't always so good.
Take second year with the rocket he launched in class so Hermione could steal potion supplies. That is actually potentially lethal if it hit someone instead of a cauldron. Even then, it's hard to say how much that messed up the potion and if the students smothered may have suffered long-lasting consequences we aren't informed of.
Then we have Harry in fifth year who staunchly refused to listen to reason before flying willy nilly towards the Ministry of Magic. He never stopped to think "Maybe I'm being played here."
In sixth year he outright blamed Snape for Sirius's death, not even getting the hint that Snape couldn't say or do anything in front of Umbridge. He just...blamed and hated him because Snape was keeping his cover. True he was a jerk while doing it, but he kept his cover.
Not to mention using a spell with unknown consequences on Malfoy and nearly killed him because he felt a kinship with the Half Blood Prince...until the end of the book when he learned the identity.
Also he expected the authorities to react as he wanted them too based on gut feelings and absolutely no proof whatsoever. Constantly calling Draco out as Death Eater, well he was right, but he acted without gathering any proof, because that's what he had always done and was oft rewarded for it (Sorcerer's Stone, hunting Sirius in the Shrieking Shack BEFORE learning the full story....where Sirius tried to kill Snape for being annoying and a snoop.)
Harry was never actually that good when you think about it. He's only under the illusion that he is.