I don't really agree with you here: from the beginning of the story we had numerous moments where the laws concerning witches and magic were questioned, if they were truly good or too restrictive. The witch's world in this serie is quite authoritarian, forbid the use of magic to heal even some basic wound is absurd, and having the monopole to such a great power isn't democratic either. However concerning Coustas's behavior, from the start the author portrayed him as a hot-blooded character who can do stupid things when pushed by strong emotion so his action isn't that much unrealistic, even though I suspect that he will turn against Ininia later on