@SuraimuSuu: "Pure" what, though? Many have used that word by itself, not realizing that it is a qualifier, focusing on the often-intended meaning "untainted with evil knowledge/inclinations".
The problem with that is that there's a difference between being morally good (as your example describes) and simply naïve. In order to do--and in so doing,
be--good, you
must know what evil is. You have to know it when you see it. To assume good of everyone around you bar none, even though some of them have openly and flagrantly demonstrated evil, is to walk down a path that leads to being evil yourself.
These magicians are obviously more competent than that loser Ditzen (loathsome character, truly). Just by going to the flying castle, they're far more likely to learn from it and/or be inspired by it--that's how technology works. And through that inspiration, Violet can enhance her golems, and use them to better bring harm to the world below.
All because Taiki thought, "Let's all have fun in the sky, eat rice, and be friends~" He doesn't have to attack the empire--I think his neutrality is a good thing--but he doesn't have to and should not grant evildoers any favors. Just setting foot on his castle grounds is one hell of a favor for almost anyone.
The sun doesn't stop shining when one closes his eyes; similarly, human nature won't change just because one wants to see the best in everyone, even those who have no good left to speak of.