It wouldn't have been to me, since to Klingons it is normal. Ben Sisko is a god, but he seemed to judgmental here. The only wrong here, as Worf himself said, was violating Starfleet regulations. Besides, Sisko as a human should know that not all human cultures have had the same views on the morality of killing. Even today, it is not so black and white, since technical homicide is not always deemed a murder in every culture.