Worf is a Federation citizen, a Starfleet officer. As such, he's subject to Federation/Starfleet law/morals. Meaning YES, Worf had no right to attempt to murder his brother, despite Kurn being suicidal (in desperate need of psychological help, not of being killed). It's still attempted murder. Sisko was VERY lenient towards Worf. Normally, such a deed would cost Worf time in prison - of course, his Starfleet career would be over. As a general policy, keeping attempted murderers in a position where they can fire WMDs (photon torpedos, etc) is NOT a good idea - unless you really want a few billion sentients to die. About attempted murder being acceptable in klingon culture - so what? Cultural relativism? This can only go so far until your behaviour - breaking your own moral values in order to appease some other culture - becomes, in effect, a betrayal of your own values, your own culture. Looking the other way while some guy kills another - just because, in their culture, it's acceptable - is most definitely going too far. The opposite view leads to absurdities: What if the victim is a member of your own culture? You look the other way because in the murderer's view, what he does is justified? What if it's your family? What if it's you - you just sit there and let someone kill you because, in his culture, what he does is OK?