If it was Remdal who's behind it and if, god forbid, somehow Jill's family got hurt in the process then Gerald is not the only one with an agenda of revenge on the man. Coul be fun in the future :3

Even if not, his stance on the darker magics makes him a direct opponent to what Jill wants. If, for instance, her efforts in defeating the Withering gave her some influence in the duchies, she would almost certainly leverage it to try and convince people that they're not as bad as they are made out to be. I can't imagine that Dennis would just idly watch that happen.