I think you are making a mistake in the discussion you had with your son. Your son might be equating (depending on how old he is) love and acceptance of human mistakes. Those are based on judgement and decisions, using an intelligent brain. People do make mistakes, and people do not kill them as punishment.
Roosters on the other hand, do not make mistakes, they have VERY LIMITED judgement, they have very small brains. They are not people, they do not have people emotions, or decision making process skills, and they are quite limited in what they can learn especially as to behavior control.
Their behavior is largely controlled by instinct and hormones, not reasoning and love. It is a human trait, to give animals human emotions, and in some animals, it is possible, but those animals have much larger brains than a chicken. With a chicken, people are just fooling themselves, when they pretend that chickens love them back, and would make decisions in the favor of the person, which is what love really is.
I do agree, that you need to discuss it with him, but he should not be part of the decision making process, that should be an adult decision based on the adults estimation of the danger. Children (and some adults) wish things could be different, and often don't have the maturity to see reality.
MrsK