[Obi-Wandreas]

BUT, HP never used dark magic knowingly

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He used cruciatus on Carrow when Carrow spat in McGonigall’s face.

Mrs VS

And notice how she didn't bat an eye about it. She tells him it was foolish to come back to school and then to defend her. At no point does she have any problem with him using one of the three unforgivable curses on a Death Eater. In fact, she proceeds then to use another unforgivable curse on him.

Since there's no talk about any sort of bad consequences for either of them, Rowling actually makes a pretty strong statement about what must be done in time of war.

We don't see any good wizards using Avada Kedavra, but I'd love to know what the fsck Mrs. Weasley used on Bellatrix. Loud, messy, and just slow enough so that they know they're being killed.

[supercat]

He used cruciatus on Carrow when Carrow spat in McGonigall’s face.

He also used the Imperius Curse at Gringotts.

Since there's no talk about any sort of bad consequences for either of them, Rowling actually makes a pretty strong statement about what must be done in time of war.

Using Unforgiveable Curses on Death Eaters might be justified, but I don't see the justification for using an Unforgiveable Curse at Gringotts. I'm pretty certain the Imperius Curse is unforgiveable, isn't it?

[Maigrey]

They inferred that Molly was using a Killing Curse. Rowling didn't come out and say it, but from the reaction, that was used - and used silently.

The words were for intimidation, where silently, they confer more power, and less opportunity for the opponent to block or avoid the spell.