Pretty much this. It's not so much a matter of Harry not using the killing curse as it is that he doesn't want to kill people other than Voldemort by any means. He doesn't even want to use a nonlethal stunning spell if knocking someone unconscious is guaranteed to cause their death under the circumstances.

And really, I think asking "Why doesn't our child protagonist want to kill people?" is a question that answers itself.

 

But he did. During the Battle of the Seven Potters, he only used the disarming spell on Stan. But did use Confrigo, Impedimenta, and Stupefy on the other Death Eaters.

 

Imperius, at least in the context he used it, came across as spur-of-the-moment desperation. They were about to get busted breaking into Gringots, and Imperius-ing that guy was the only way to keep their cover from being blown.

Now, the handling of Harry using the Cruciatus curse is much stranger to me. Since it seems like the universal theme when Harry breaks it out is that he's pissed off and wants to hurt the target. Especially with the added component of him eventually learning how to "mean" the spell.

Yeah, Deathly Hallows seemed to treat the unforgivables as less dark arts or evil magic and more wartime magic that's not normally okay in civilized society. The Killing Curse is illegal because casting it on a human being means you killed them, and outside wartime that's much harder to justify. Thus, Harry's willingness to use the other two unforgivables is a sign of him accepting wartime morality, but not using the killing curse was him trying to hold on to some level of innocence. Maybe?

 

Please don't open doors that can't be closed.

 

Sorry.



To get back on topic, the question of why Harry *did* use the other two Unforgivables is a good one. Desperation played a role during the Gringotts mission, I agree. For the Cruciatus, I‘d go with a spur-of-the-moment decision in the face of one of his favourite teachers being threatened and insulted, and Carrow getting a taste of his own medicine.

It is also worth to point out that when Harry successfully cast his Unforgivables, they were not technically illegal anymore, which could feed into the wartime angle angle @Chengar Qordath mentioned.

 

I think Harry’s use of the other two unforgivables is both overlooked and underlooked by different sections of the fandom. It doesn’t make him into some crazy edgelord, but it also definitely denotes that Harry has few qualms about his use of darker magic.

There was basically no indication that he failed to cast either the cruciatius or imperius I’m Deathly Hallows. While the war time angle helps explain some, I think it really could be used as an avenue for a logical progressioneven farther If you had a story where Voldemort doesn’t die at Hogwarts and Harry has to continue fighting in perhaps more active role against his enemies.

 

Good point, but in terms of personal preference, I’d rather have a well thought-out new threat than Voldemort again. That does get old after a while. Include some irredeemable Death Eaters (canon characters or OCs), but I am of the school of thought that Voldemort conflicts should be confined, roughly, to the timeframe of the seven books, with Hogwarts as the climax. That was one of the better narrative decisions from Deathly Hallows, at least in terms of drama provided.

 

The fact is that Harry, as someone 'raised' in the muggle world, has a distinct disadvantage when trying to perform the Killing Curse.

When he tries to say "Avada Kedavra" he always accidentally says the muggle magicians' phrase "Abracadabra!"

This is canon, I assure you...

 

]The Deathly Hallows are perfect for this. Harry could slowly be corrupted by using the Resurrection Stone and Elder Wand.

 

Except that the only even remotely corrupting properties evinced by either are chronic depression and recklessness, respectively.

 

Or Harry could become obsessed with using the Stone, slowly becoming detached from the living, then consumed with speaking to historical figures (Man and No-Maj) to gain knowledge, ultimately leading him down a rabbit hole of questionable morals. Think about how Harry was when he found the HBP book, or his obsession with the Hallows.

Now he has a source if unlimited information from the most powerful wizards ever...

 

If you want to cause pain to someone, then the cruciatus curse is definitely the way to go. There's other spells for causing pain, but this is THE pain spell. Setting someone on fire, breaking bones, conjuring bullet ants, they would all leave damage that needs dealing with, and potentially their own incant/wand motions. And they probably don't cause the same unbearable agony that can, quite literally, drive you insane.

If you want to control someone utterly, then the Imperius is the curse for you! There's probably other ways of forcing control, but I can't imagine they'd be quite as easy to implement. The first one to spring to mind is making someone agree to an unbreakable oath to follow your orders, but that would likely require forcing them into it, and gives them an out (by ignoring an order, and therefore dying). Love potions could maybe help, but again, they wouldn't be anywhere near as quick, or efficient.

The killing curse is really good at killing people. If it hits them, then they normally die. If it hits their leg, or their finger, or their head... They have ceased to be.
But (borrowing from bad fanon) other ways of killing people exist. A piercing curse through the head or chest would likely kill you. An explosive hex could kill you. Knockback from an expilliarmus could kill you. Being levitated and dropped out the window, or having a club dropped on your head could kill you. Being burnt to a crisp by fiendfyre could kill you.
Yes, these can be blocked, or countered, or just survived. But if you animate statues into the way of each one, you're going to run out of statues really quick, so you have to actually work at dealing with each one individually.