User blog comment:Miskos3/Episode 272: Fairy Tail Zerø: The One Who Teaches Magic, Review/@comment-190.58.249.5-20160221003339/@comment-7418318-20160221225607

Once again: For feelings truth does not matter one bit (unless you thorouly think about matter and consequences). Feelings are internal.

And thus it does not matter if it's based on a lie or on something evil or anything else really. It only matters what the being him-/her-/itself beliefes and feels.

Just look at Fairy Law to see that this is the case not just in reality but also in Fairy Tail. If the wielder truly believes in his mind and heart both that a person or being is an enemy, that enemy will be destroyed (or at least hit and severely harmed), no matter if that person is good or bad in reality. It only counts what the wielder thinks and feels.

Yes in the end Laxus didn't kill anyone, but only because his conscious mind and his emotions were out of synch. Freed even said so, that in his heart Laxus didn't really want to kill anyone, even if he conciously chose to. But if he had truly believed that the people of Magnolia deserved death or that their death were justified or necessary, he'd have slaughtered them all with a spell that was created to protect the guild.

It's all about perception, believes and feelings, not truth.

Or take Natsu as another example. Would you say that killing a person is "something positive, and not negative"?

Even under the most extreme conditions Natsu refused to kill before, but in this war he tried to kill Zeref. He was willing to do something he himself clearly believes to be bad if not outright evil. And yet he still poured all his power of feelings into the attack anyway. Sure it had a "positive" component too with protecting the guild and continent, but it was still far from pure positive. But in Natsu's perception this evil deed was still justified due to the stakes and circumstances.

I should have thought of that as an example earlier...