Hey There SISKO -
I hear what you are saying, however, I stick to my course of action based on the following reasons:
1. Star Fleet Command is fully provisioned to deal with the situation of KAHN and his people. As I am not cut off from communications with SFC in this situation it is not within my authority to usurp the jurisdiction of SFC, and thereby act as a judge, jury, and/or executioner. To put it simply, in this case - being in communication to higher authority - deciding KAHN's fate is therefore not my job; only his delivery.
2. Added whatever past issues need to be addressed, KAHN now gets to add the very current charges of commandeering a Federation vessel, and in doing so, endangering the lives of all hands on board.
3. The concern that turning KAHN into the authorities will mean an automatic 'Death Sentence' is pure speculation and opinion. One would think that SFC has the wisdom to deal with his special situation and history; and again, as a Starship Captain, it is not my job to speculate if I personally feel SFC will have that wisdom - wisdom also being defined by my personal opinion.
4. The fact that KAHN is a genetically altered being through no fault of his own, is no more my concern regarding the discharge of my duties, any more than if he was human, Vulcan, Andorian, or what have you; as no one gets to decide their own creation - and again it is a moot point in relation to the execution of the orders I have sworn to uphold.
So,.. that about sums up my rational as to why I DO NOT give KAHN a court-martial, or place him on the planet.