im looking at it this way...
STII - kirk offers kahn the opportunity to surrender, live and stat trial and sentencing for war crimes... kahn uses opportunity to try and kill kirk with genesis, kirk even tries to beam aboard to stop it but is told he cant
STIII - kirk tries to offer kruge a hand while on the mountain cliff... kruge uses opportunity to try an pull kirk off the ledge first, kirk saves himself by killing kruge
STVI - kirk finally finds the ship that has been trying to destroy his... after a lucky shot, kirk (and sulu) destroy the BoP to prevent it from recloaking and being difficult to detect again. oh and he prevents a full out war that would have resulted should the assassin be successful.
seems like kirk learned over the first two situations that offering a chance leads to being attacked again and put into a life or death situation that could cost countless lives.
STXI - kirk knows that nero's ship survived a direct ramming by another federation ship to come back and kill millions of people (he read pikes dissertation)... kirk still offers help but when forced to be judge and jury (nero basically pled guilty and showed no remorse) he finds nero guilty and proceeds with sentencing which in this case is death.