I think the utility-maximizing reasons to avoid disproportionate punishment in such cases among humans have more to do with likely perpetrators being somewhat blind to such disincentives (remember, these are people who attack others by killing themselves,) and the fact that nations operate in a reputation system where acts of disproportionality which are too large tend to attract negative reputation.

Since humans tend to operate under friendship/anger/fairness formulations rather than utility maximizing ones, a sultan who honors a precommitment to cut off the head of a man who elopes with his daughter is seen as reasonable in circumstances (including a historically common degree of protectiveness of one's offspring) where one who massacred the man's entire village to be even more sure of deterring other attempts to cross him would be viewed as cruel and tyrannical.