Darken knows what Kahlan is capable of when she has control over her powers - he saw her go into the Con Dar. Why on earth would he not respect his daughter's abilities? Very troubling. Darken's not really thinking of his children as threats equivalent with how powerful he expects them to be--kind of a, he raised them so they won't turn against him assumption (the same problem he runs into with Nicholas in canon Reckoning, I think.)

Also, this story definitely highlights some of the sexism inherent in the Rahl system. If nothing else, Nila is the eldest, but Nicholas is the heir.