Everyone talking about the evil church trope, but I'm actually willing to let it slide in this story. Everyone's initial reaction to Zagan is that hes not a good person, to the point where they end up genuinely surprised at the fact that hed save them from bandits and the like. And judging from the info we've been given, it seems like Zagan's kindness is the exception to the rule; while he looks down on anyone who would sacrifice people as a means to an end (when he kills people, he does so because that's his goal, not the requirement for the goal), even his best 'friend' was all but willing to do basically anything to boost his power, including sacrificing the very knight that Zagan went out of his way to save. So the church official confidently giving the order to execute Zagan isnt out of place; mages in general seem to be a legitimate threat to the public.