Flamme's Shame
Demons shamelessly manipulate and murder humans by using human words deceptively.
So why is it considered shameful for Flamme, Frieren, and Fern to manipulate and murder demons by using their "native language" of magic deceptively? It's not like they are doing this to trick and defeat other honorable mages in formal battles or anything - just tricking bloodthirsty evil beasts who would otherwise literally devour them and their offspring without a care in the world.
How is this, in Flamme's words, "making a mockery of magic?"
I've only seen the anime series btw, so if it is explained at some point in the manga, please don't spoil it for me.