"They'll have to be a quest, sooner or later - that or we'll to war again, though no sane man wishes that. But the king sees his own goodness in every man, imagines them content to sit and discuss ideas endlessly, to restrict their feats of arms to jousts and rescuing the odd innocent in distress." That's a center that can't hold, and Kay knows Arthur knows it. The king knows his knights as well as Kay does; he just has more faith in their ability to change.