[Maigrey]

What it is showing is that, even with the "ends justifying the means" is that there are failings of the main characters, breaking their own personal moral standards to achieve the ultimate goal of stopping Moldy Voldy.

Personally, I would call that the basest form of integrity: doing what is necessary to achieve yout goal, regardless of personal cost.

Harry was willing to go to Azkaban, and as he showed, willing to die, to achieve his goal, regardless of personal cost. And, when he did use the unforgiviable curses, he was, if you could do such, gentle with them, until he came across The Carrows insulting Prof. Minerva. Then, he did what was needed to stop them against her.

[SuziQ]

And, when he did use the unforgiviable curses, he was, if you could do such, gentle with them, until he came across The Carrows insulting Prof. Minerva. Then, he did what was needed to stop them against her.

It wasn't just him insulting Minerva; it was everything he'd learned about what the Carrows were doing at the school that caused such anger in Harry.