Of the adjectives that are given in the first answer, I agree most with "bland." Of course, that describes pretty much everyone in their society so I do not know if it is very helpful.
The only things that I would add to the first answer are the words "deceptive" and "oblivious."
I would say that Jonas's dad is deceptive because he does not really say what is involved in releasing a baby. He fools Jonas and the others into believing it is something nice.
I would say he is oblivious because he is not aware of how nasty his actions and his society are.
In the book The Giver Jonas father works in the nursery taking care of the infants but one of the deeds that he has to do is to put them to death sometimes. He refers to the act as releasing the infants. I can think of quite a few adjectives that would describe his father in the story.
Nurturing, ignorant, caring, trustworthy, parental, dutiful, obedient, friendly, helpful, unengaged, and bland.
Some of the traits are evident because he has no memories of how to have real emotions like the rest of the members in the community. I can not call him a murderer because he does not "kill" according to the communications of his society.