You know how much I dislike the George R. R. "Can't Finish a Book to Save my Life" Martin "there are no heroes, everyone is morally grey" trope. You can err in the other direction, though, and make the hero just too pure. When a hero falls, I mean really falls, and does something he'll regret for the rest of his life, something he can never take back nor truly make up for, it can become an enduring lesson in moral humility and make him strong. St. Peter, in his darkest hour, denied Christ. This doesn't make him Judas. It makes him, after going through the fire, the prince of all the Saints. I think it makes Harry a deeper character if he has done a thing he can never take back, something he has to live with for the rest of his life. It also makes more sense in the Draconia AU because it creates a degree of balance: she has done some heinous stuff. It's complicated, of course, from her upbringing, her family's expectations, Voldemort's threats and manipulations. But she still did it. Sectumsempra gives Harry a perspective where he can more naturally forgive her for the various things she's done, because he also has done something he feels to be unforgivable. There's a lot of talk in the books about Unforgivable Curses, but this is primarily a legal category in HP. They are not actually treated as "curses which are absolutely evil and no non-evil person would ever use them," because that's simply not what the are. Harry uses 2 of the 3 in book 7, and it isn't treated as a big deal or as compromising his moral character deeply. They're tools. The AK curse is just a gun. They're neutral. It all depends on how you use them and why. Sectumsempra is morally neutral too. It wasn't the casting, it was the consequences. In the Draconia/SS timeline, Harry isn't even morally unjustified in casting the damned thing. She is in the middle of throwing a Crutiatus at him, which certainly justifies a Sectumsempra if you know what it does, and justifies a spell that you don't know what it does too. (I am setting aside that in the Draconia/SS timeline, although she TRIES to cast a Crucio at Harry, she fails, because she can't do it: she doesn't hate him enough to WANT him to suffer. This is true and important, but HE doesn't know that. It happens too fast. He only hears her start with "Cruci—".) On the surface, Harry hasn't even done anything strictly wrong — stupid and reckless? maybe. But wouldn't you use an unknown spell if it was all you had when someone's aiming a torture curse at you? People could even tell him this. That he was justified. That he didn't do anything wrong here. He's a hero. But Harry knows he did something wrong, something unforgivable. He can't take it back. He can only resolve never to do something like that again, no matter what. He will not hide behind "It was technically justified, because it was self-defense. Her injuries, while unfortunate and more than I meant to do, don't really reflect badly on me." One of the serious deficiencies in the Harry Potter books is that there isn't very much of a redemption arc. There's Snape, but his loyalties and decisions are complicated. It isn't a clear and decisive turn away from the darkness. Draconia can do that. She can really repent. That has weight. Harry needs to be able to meet her there too. And that means he has to understand what it is to have done something unforgivable, and ask for forgiveness anyway. Preferably done something unforgivable to her. "Preferably" in terms of the story, the narrative. Contrary to that twatwaffle who was calling the SS scene "torture porn," you don't do this Draconia or to Harry because we enjoy their suffering. You do it because stories are about human beings, and sin and redemption are at the core of that. You do this to these two so that later on they can truly unite, the two of them holding a single wand and destroy the dark lord. You do Sectumsempra so you can have Two Hearts, One Wand. You show them HERE, at their lowest points, so when you see them much later, married and surrounded by at least 8 kids, you can appreciate more deeply what that MEANS.