His lamented father was, if he's being honest (and he rarely is, when it comes to Uther Pendragon), an aggressor. Uther Pendragon rose up and conquered Camelot, uniting disparate and squabbling minor territories. When he was opposed, he fought until his enemies were destroyed. When the use of magic killed his wife even as it begot him a son, he waged war with a vengeance that was never sated during his lifetime. He slew nearly every dragon, nearly every dragonlord, and had any accused of witchcraft put to death. He nearly blotted the old religion out of existence. He ordered massacres on peaceful peoples. He was full of a fury so terrible even his children feared to defy him.

You could say Arthur's a little sensitive about this.

Which is why he turns, pointing a finger in Byerly's face, and hisses, "Do you have a purpose to your prattling, or do you just enjoy the sound of your own voice?"

To his credit, his voice is kept lower he might've done otherwise, somewhat mindful of the danger at hand.