Harry's Use of an Unforgivable Curse

[nepenthales]

No: HPFGUIDX 96218

Forgive me for jumping into the conversation with no specific point 
of contention to address, but I'd just like to mention a few things 
that stuck out to me when I read the scene.

Firstly, I don't believe there will be any immediate ramifications, 
legal or otherwise, for Harry's use of crucio on Bellatrix. 
Whether or not the act was legal, moral, justifiable, or whatever 
else is not particularly significant in the context of the larger 
story.  I don't think we will see evidence that anyone but Harry
is even aware that it happened. (Dumbledore might have been watching, 
but I think he would wait to see how Harry reacts to his own behavior 
rather than confront him immediately.)  It will surely be something 
over which Harry agonizes in book 6, which makes him question 
himself, and which he will need to come to terms with; these things 
will help to define his character, and so will the eventual admission 
of his deed to whomever may be present when he comes to grips with 
it, but the conflict within Harry that inspired his violence will not 
be resolved.

So, what is the point if nothing will be resolved?  The point is to 
show us that Harry is being faced with circumstances that could lead 
him to become the very things against which he is fighting and that 
those circumstances have had a real effect.  If this pattern of 
behavior continues and Harry becomes complacent with using the Dark 
Arts (and the Unforgivables especially) to achieve his ends, then he 
may defeat Voldemort only to take his place.  Note that this does not 
suggest that Harry will hold the same ideals as Voldemort, but that 
Harry will essentially become a Dark Lord who will try to force his 
own ideals on others with the same methods.  Building up this 
internal conflict is essential for his future choices to have any 
meaning.  If there is no conflict within Harry, then a decision in 
the end to do the right thing has no weight.  If Harry always did the 
right thing, then his eventual development into a morally-sound man 
would be unquestioned.  That would be neither interesting nor 
realistic.  It is much more powerful that he must constantly fight 
the temptations of his negative feelings and desires; and if, in the 
end, his character is put to the test, his ability to overcome those 
feeling and desires will make him all the more a hero.

-Nepenthales, fighting with all his might the temptation to post a 
treatise on the similarities between Harry's mission to the DoM
with Luke's trip to Cloud City